Early ... Intro Picture

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Interview with Professor John N. Murrell

University of Sussex, Brighton, May 17, 2000; 11:00

Early beginnings

Dr. Anders: Professor Murrell, first things first, you were born in?

Prof. Murrell: 1932.

A: You have, to my present knowledge, written at least four books (1-4). Have you written any more?

M: Yes, a few more {laughs}. But not on this topic. Quite a different topic.

A: How many publications do you have, professor Murrell?

M: Three hundred and something. (5-23) , (24-64)

A: And do you consider yourself a second generation quantum chemist or first generation? Of course it depends on how one wants to count...

M: Well, it depends on definition. In fact in a way I'm third generation because the father of British quantum chemistry was Lennard-Jones   (65-81).

Lennard-Jones had a student called Coulson.   (131-138).

Coulson had a student called Longuet-Higgins {these linked bibliographical notes are from the present author's archive - they seem to be no longer available from the originators.}.   (181-198).

And I was a student of Longuet-Higgins as fourth generation. But I started about 1955 to do my Ph.D. with Longuet-Higgins.

Thesis using PP

A: About what was your thesis?

M: It was primarily on organic spectroscopy. I don't remember the precise title, but it was really using the first Pariser  - Parr type calculations (251-258) for organic spectra with a few adjustments. That was about 1955/1956. There is quite a lot published. There was a series of papers by Longuet-Higgins (181-187) . The first of the series was actually with Michael Dewar, they discussed benzenoid spectra (281). And I joined on to that research project and we wrote a - my guess is about seven, eight papers on that subject in the early days (5-8) . And I also worked with Pople, (9) I started one year - Longuet-Higgins was in King's College, London, and then he moved to take the chair of Cambridge because Lennard-Jones died. So I moved as his student to Cambridge and did another two years to write up my PhD. And at Cambridge at that time there were two other people important in semiempirical theory, one was Pople, (282) and the other was George Hall (283) . I did some collaborative work with Pople at the time (9) , not with Hall although I kept in touch with him over the years.

A: And so you have been a chemist, physical chemist or physicist?

M: I worked in several physics departments and several chemistry departments. But I think, I'm a chemist really. I've been a professor of chemistry here for 35 years. A long time, I've now retired.


A: How do you remember these people, if I may ask you now down the list. Let's say Lennard-Jones.

M: I never met Lennard-Jones, no, he died before I quite got there. My supervisor Longuet-Higgins is actually still active in Brighton, here. He turned to the subject of artificial intelligence about 25 to 30 years ago.

A: Why did he do that?

M: It is a very interesting question. But he felt that he had done enough in chemistry, I think, theoretical chemistry. Also at that time he was quite strongly opposed to the use of computers for analysing chemical results. He was always an analytical person. That's also my training. Interestingly, when he moved to artificial intelligence the thing he became interested in was computers. But he never used computers for chemical problems up to the time that he left. A brilliant analytical theoretical chemist, say, and not just in molecular orbital theory. He did a terribly important work in statistical mechanics and in symmetry for example, a very influential man.

A: He himself was a physicist?

M: He was a chemist, a graduate of Oxford and a student with Charles Coulson at Oxford. Coulson himself was a mathematician.

Lennard Jones

A: How would you consider the influence, let's call it the chain of influencing people? Did Lennard-Jones take up ideas of Hückel or did he work simultaneously in a way?

M: Well, Lennard-Jones wrote very important papers from about 1928 onwards right at the beginning of the subject (65-70) . He was the first one for example to explain in molecular orbital theory why the oxygen molecule was paramagnetic (70) . It was a seminal real key solution. And he also wrote a paper bringing together molecular orbital theory and valence bond theory at that time (XXX) . So that was his early 1930ies work. And then later on he did important work also in statistical mechanics (XXX) . You know, the theory of liquids was much influenced by Lennard-Jones potentials for molecular forces (XXX) . It's very much - or it was the tradition of British theoretical chemistry, and particularly the Cambridge group, to treat the subject of the mathematical analysis of chemistry on a very broad front. They weren't just molecular orbital people, they weren’t just quantum people, they brought all tools of analysis to bear on chemical problems. And I think a few people who kept it up, I mean, Pople himself kept it up enormously, very much the same thing. Not an easy thing to do, actually. I liked to think but I've done a bit, I mean I'm not just an orbital man. But it was the training we had in Cambridge.

The Cambridge School

A: In Britain, did that mean just to go on with theory or do applications like the Pullmans in Paris?

M: Another strand, I think, is quite important in the British school, was that the problems were driven by experiments. I don't think, at least in the Cambridge school, that there was so much interest in the fundamentals. Let me take an example. Anybody in the electronic structure theory gets involved in the electron correlation problem. And you can bring very heavy analytical mathematical tools to bear on that, group theory and things. I don't think that was the way it was done – in Cambridge with a few of exceptions, I think Lennard-Jones did a bit of work like that but not Longuet-Higgins. He is an exceedingly competent mathematical person but I would say that almost all his work was driven by an experimental result in spectroscopy or something like that. He worked closely with people like Herzberg for example (284). and the other was George Hall . Orgel was closely involved with transition metal spectroscopy (285-286). So, we were much encouraged to do something which other people were going to find useful.

Now, the electronic spectra of organic molecules was done because here was this great mass of organic chemists doing spectroscopy so what could you say that might be helpful. I think, that was their driving force above the simply analytical.

QC and tools

A: But in that paper of yours - did you think more of mathematics or more in terms of concepts (XXX) ?

M: Well, the tools don't get totally separated. But I'm sure it is connected to the development of the subject. At a time when the computational tools were very modest, it was more and more important to build up models and concepts, because that was the only way you could get numbers out. The tendency nowadays is that there is a big computer and you put input and out comes output, you know, you don't quite have to think about it somehow.

So most of the concepts of theoretical chemistry which are taught to students nowadays a considerable number come from the 1930ies to 1950ies before computing really got into its sway. That's almost inevitable. When people like Dirac in 1930 said, that chemistry is solved (XXX) , we've only had to look get the calculations done. But it took another 30 years before it was achieved. Well, I think, we have concepts and ideas. People don't do semiempirical theory now to save computing time, you are doing it so that you can think about ideas using those particular models.

A: To some extent industry is doing that.

M: Yes, you go to bigger and bigger systems, that's been an interesting development in industry, the role of theory and the role of modelling. There was a time,certainly when the pharmaceutical industry thought that modelling would be terribly important. It probably still is but I don't think they believe so much in many of the computational techniques that get to that level, and I wouldn't believe them either.

A: It's maybe a question of costs.

M: No, I think it's not cost. Because it's terribly cheap, it's terribly cheap to do calculations compared with doing experiments.

A: A theoretician at Novartis , Karfunkel, maintained though that in order to solve a question, let's say in the case of a kinetic reaction, and he said that it is very quickly 20.000 Swiss Franks for a job like that. And that would only be for one simple answer, not for an all-around evaluation.

M: Particularly if he doesn't believe the answer at the end {laughs amused}. Yes, on the other you hand you have a modest computer and you switch it on at night and you come back in the morning and there is perhaps an answer. I mean, all of this - what is the real cost is thinking about the problem {stills laughs in thinking of the one before}, it needs still people and minds, that is the costly thing. Computing is for free.

Personal development (1)

A: Now, your personal development, how did you arrive - you went to the university, how would you describe your development towards theoretical chemistry.

M: Well, I did a degree in chemistry and in the British system at the end of your first degree you look around for PhD projects, and it was quite by accident that Longuet-Higgins was in the physics department in my university and there was a little notice up on the board saying if anyone is interested in doing theoretical chemistry with Longuet-Higgins would they go and see him. And I must have done that.

But in my chemistry undergraduate course, I'd really been interested in the mathematical side and I'm not sure why, I should have been a mathematician probably. It's not that I know much math but it comes pretty easy to me in analytical work. So I went to Longuet-Higgins and I had intention to do statistical mechanics which is one of the areas he was in.

But the first problem he set me was doing Hückel calculations. And my first three months I worked out the Hückel orbitals of things like anthracene, you know, just to get my hand in, just using log tables and things like that. (287). And then, after I'd done that, I remember after Christmas in my first year, we started talking about spectroscopy and putting in electron correlation and that led to several papers.

About two years later I remember Longuet-Higgins saying to me "well, I'm sorry, we never did get around to statistical mechanics" {laughs hilariously}. In fact, it took me a long time to do that and eventually in my own new researches I moved on to things like scattering theory of atoms and molecules and theories of liquids. So I broadened out a lot, but all my early work was straight molecular orbital theory.

And I got a PhD and then I went to work with Mulliken.

Personal development (2) at Mulliken's

A: How long had you been there?

M: I was only one year with Mulliken, which was a very interesting place to be, not so much Mulliken himself, he was a very interesting fellow but not easy to talk to, actually.

But the Chicago group at that time was very lively and there were two people in particular, one was a fellow called John Platt, who did a lot of analytical work on spectroscopy and had his own nomenclatures and things (288). . And the other one was Clemens Roothaan who was developing the ab initio techniques in those days (XXX) . So Chicago was a great place to work and also during this year another person that I met who was influential was Michael Kasha. He was an important spectroscopist. He was actually down in Florida then at Tallahassee, but I met him and we kept good friends ever since and I did postdoctoral things with him (XXX) .

Now, I was only in Chicago for one year and then I came back to Cambridge and had a junior college and university post of three years, more or less as an independent worker. But that was still the time when people like Pople and Orgel and Griffith (293). and Boys (294) were at Cambridge. Then there was an expansion in British university system and in particular Porter from Sheffield, Lord Porter, was looking for young people at Sheffield, and I went with several other people from different parts from the country, but I went as the theoretical chemists to Porter's group in Sheffield and stayed there for four years.

A: Was that at McWeeny's time?

M: Before McWeeny . McWeeny followed me. I left and McWeeny came in. Although I never worked closely with Porter, he was very influential and friendly and helpful and encouraging. And there were quite a number of other people around at that time, that I had very good interaction with.

A: How was that interaction, were there seminars?

M: Yes, just casual, just around the lab. We used to meet with coffee all the time.

A: And you exchanged problems?

M: Yes, absolutely. It used to be a weekly seminar, called coffee and kinetics run by George Porter at which anything went, you know. It was half a dozen really top class young people at that time in Sheffield. Most of which then disappeared to get professorships elsewhere.

Then the other thing that was terribly important at that time which - it sounds extraordinary now - but there were a lot of young people and wanting to do PhDs in theoretical chemistry. That was about the beginning of 1960/1962, something like that. In two years, I think I had a research group of about ten people. It sounds unbelievable, you know, now my colleagues now if they get one student, I think they are lucky. I had this huge research group {laughs}all doing different sorts of things. And many of them are also now quite influential people.

A: Like?

M: Well, one is a lecturer in Sheffield now called Cook, who is a theoretical chemist (295-297) . There is another one in UMIST called Hinchliff (298-299) . There are a couple of Portuguese, there is someone from Croatia, Trinastic, (300-304) I mean, I had people all over the world.

A: Trinastic?

M: Yes, he was a sort of postdoc with me and Randic (305) , he was as well postdoc with me. He went to the States, to Iowa. So I had this terrific group, and then I came down to Sussex about 35 years ago as a professor.

And again I had a very large group for many years and some really top class people, you know. I had marvellous students {laughs}, I was very, very lucky. I Don't know if you have met Paul Madden in Oxford, he is a professor in physical chemistry. There is Jonathan Tennyson who is a professor in University College, London, David Clary at the same place, I had excellent students from all over the world. I was marvellously lucky, you know, you couldn't do it now, no matter how good you are. You wouldn't get people who want to come into the field in the same way.

The state of Quantum Chemistry nowadays

A: Another question. What is the state of quantum chemistry nowadays?

M: Well, I think, to some extent it is like NMR, it's part of the analytical tool for most people, isn't it? But of course, if you want to judge your results, not just get results, then you still need to know a bit of the background. You must understand what you're doing, it's not just a matter of computing. I do a lot of computing and have done for years and my students have. But my first attitude is, well, let us be sceptical - these are numbers and what we are going to do with them. Well, as I think, if you are not trained as a theoretical chemist, trained in quantum chemistry, you tend to think that numbers must be right, they come out of the computer and therefore they are good numbers. My attitude is they are probably not {laughs}. Let's argue as to why they are useful.

A: What about numbers and organic chemists and applications? I always get to hear that quantum chemistry is an additional nice touch when you write a thesis, as a posterior thing. One uses some Extended Hückel program (XXX) . If it fits, alright, if it doesn't one forgets about it and uses something else.

M: Well, I think it does, it should help people to think about what they are doing. I don't oppose it any more than I oppose someone doing an X-ray structure or an NMR, you know, it is a question what you do with it.

But we had a visitor last week, a spectroscopist from America, called Robin Hochstrasser, who is about the same generation as I am, and we were talking about modern developments and how easy things were and I was saying to him, well, I guess, that now if you really wanted to know something about the absorption spectrum of ethylene, you could do it on the computer. And he thought a bit and he said, well, I don't know if it is that easy. Maybe what was said in 1955 is as good as what could be said now. Not all problems are susceptible to hitting it with the computer.

A: Do you think, that organic chemistry is influenced by quantum chemistry?

M: Well, it has been, in terms of the language and in terms of the teaching. You've got to take a subject like Woodward-Hoffmann for example (XXX) . No undergraduate course, could be done without doing Woodward - Hoffmann rules. On the other hand certain other bits of theoretical chemistry have dropped out. In our organic chemistry courses students learn something about orbitals.

A: Because chemistry isn't it turning more and more into technology, a sort of putting all things together and seeing what comes out. Combinatorial chemistry?

M: Yes, combinatorial chemistry, yes. I must say, that is a topic that I find a bit strange....

What I was going to say, is that if things were totally automatic you wouldn't have some people who were better at it than others. You still do have stars; you do still have people who get Nobel prices. And that means it's not automatic. And primarily that's because ideas are still key things at the fore front of subjects.

The end of Science?

A: So we haven't reached the end of chemistry yet?

M: Well, I got the book "The End of Science" (306) , which argues along those lines {laughs}. But no, well, I don't believe it of course. It's good fun to read but I don't believe it. But if I was starting again {laughs} I suspect I wouldn't go into quantum chemistry. I don't know what I would do, it is not as easy as that, is it? It just happens to be something I'm able to do and you keep going because you have certain skills {laughs}.

A: It is said that the ideas die with the carriers of these ideas?

M: Well, it’s a bit like genetics. Your genes are from your mother and father, I produced lots of offspring around the world and I'm still going on. So some of them are doing very nice work {laughs}, but they are not doing exactly what I was doing which is also right and proper. Subjects develop.

A: In your paper here you argue that well, there are all those beautiful concepts of bonding etc. connected with the development of semiempirical ideas. Are there any effects left to be explained in chemistry?

M: So, that's the question, isn't it? Do we get shut up sharp, yes that is the question? My attitude always is that the most interesting thing is that which I happened to be interested in at the moment {laughs}. Which is the only way to operate, really. If you are not interested in what you are doing you can pack up. So in our field I happen to be currently interested in clusters and nano technology. Well, I think, there are still unanswered questions and some I don't know how to do.

A: So, can you push your theoretical ideas as far as we like?

M: Yes, there are various developments. One I think that is quite interesting is in material sciences. If you call on the material science group in Oxford, you would find that there is a whole group there who are interested in applying Hückel type models to structured materials. And doing no more in a numerical way than was done by Hückel himself, with quite encouraging results. I mean, I'm actually a great believer, I am a great admirer of Hückel theory. It sounds terribly old and out of date. But it's marvellous and it's pedagogical lovely of course.

A: In France there are books which were published around 1997, still devoted entirely to the topic of Hückel, for teaching of course (307).

M: I agree. But the thing that often makes me a little bit unhappy is when I see a problem being done in a very complicated manner and not giving any more insight than when it was done in Hückel theory {laughs}. This is the principle that you always use the simplest method to do the necessary analysis and only if that fails you go onto something tougher. That's been some of my general principles. I was recently fiddleing around with something called local mode analysis, well, I don't want to get into the detail but I actually went back to Hückel theory of butadiene and picked out the numbers and put them in and on the back of an envelope, you know, I got some quite nice answers {laughs}. I'm really quite happy. Unfortunately I asked my collegue down the road to do an ab initio calculation on it {laughs} and she gave me the wrong answer and now I don't know what to do, you see. I shouldn't have asked that it was done because the answer she got is not the one I want. It is all a question of dipole moments of the radicals and I got the right answer to agree with experiment, she got a heavy calculation and got the wrong answer. And I mean, that makes it difficult to publish, doesn't it. You know, I can't say, well, this very simple model gives me right but I don't know why she is wrong. So I just sit on it for a while, something might happen. I don't mind any more why {laughs hilariously}.

Kuhn and Dewar and different concepts

A: That is an approach nearly word by word what once Kuhn said about the electron gas theory. Sometimes he does the calculation in exactly the same way, he says, "well, I can also get the answer, maybe even better concerning the spectra".

M: Yes, {reflecting for a moment} I just think, you have got to be a bit careful and sometimes ... Just because you get the right answer doesn't mean to say it is the right analysis ... Always you have got to look at this analysis and think is this an accident or is it really valuable.

A: Another thing that ab initio people maintain is that if one fits parameters in one context one could be far off in another one. In your paper, when you talked about Dewar and NDO (XXX) you mentioned that he used six or nine parameters. How do you view that? I mean by adjusting that many parameters, isn't it that I can get any result?

M: Well, I don't think, you would get any result, that's going too far, but on the other hand I think you are in some danger of going from a good result to an incorrect interpretation.

And Dewar was really the biggest practitioner in this particular field, and {reflecting for a moment} Michael was a great scientist in many respects, but he would one year come along with this marvellous theory, you know, and he would explain how terrific it was, and in the next year he would come along with another theory and it would be a bit more complicated but different because in the last year he found that his theory made water a linear molecule or something. So people got a bit sceptical.

And the other thing is that if you are in the semiempirical game you have parameters, and have to realize that there is a body of data on which you base this work. And if all you do is confine yourself to this body of data you never get out. So, the question is, can you get outside the body and say something important. And that's the test and sometimes you can and sometimes it's not so obvious you can. So I think you have to be a bit careful in that ... Yeah, I mean, I don't think Dewar's work is going to live actually, you see. Hückel theory will live longer than Dewar's work {laughs}, in my feeling.

A: I read Dewar's biography (308) and ...

M: I wrote his orbituary for the Royal Society, I'll give you a copy before you go (XXX) . But he was a great fun man, a great man to write an orbituary on.

A: Löwdin told me a nice story concerning Dewar:

"He came to Gainesville, Florida, in the last few years he had to live and I had a volume in his honor in the International Journal of Quantum Chemistry and I asked Dewar to write an introduction. So I read it and I went back and said: "Michael, the fight is over, you have won. You don't have to fight any longer (Löwdin chuckled, reminiscing,I's.n.).
You can just enjoy your victories."
"You mean what you've said?"
"And I have to rewrite the introduction?"
and he did, in a much more friendlier way, so to say."

M: Yes, he was always ready for the battle. I liked him a lot, not an easy man, you know.

A: Where did he teach in England?

M: He had a very strange career which, when you read my orbituary, you will discover that he only had one teaching job. He went straight into a professorship in England at Queen Mary College and then he left there to got to Chicago.

Dewar was an "Oxford Intellectual"

A: He was a strong organic chemist. How did he arrive at theory?

M: He moved from being wholly sceptical about theory to being totally sold on it. And his early work -, he had a good analytical mind, so he did some very important structural work in synthesis. But he was not much of an experimentalist. He would never have made a great synthetical organic chemist but he had a fantastic memory also, a great analytical mind, he was said to be a terrific chess player for example. He was an Oxford intellectual {laughs}.

A: Can you be more specific?

M: I mean, there are a terrible lot of these Oxford intellectuals {laughs}. You know, they don't always work very hard. The idea is as you sit around and think a little bit. Half an hours good thinking a day is a good days work {laughs hilariously}.

A: That progresses from generation to generation?

M: Yes, I'm sure it does, but probably less than it used to be. I used to know another good friend, who died young, Bill Moffitt (309-311) , he was the Longuet-Higgins generation before me, but he was another splendid Oxford product, who went on to Harvard. Probably the exception is Pople, but Pople was a product of Cambridge. Pople is a mathematician of Cambridge. He was different.

Murrell talks about how to write successfully

A: Now to your books. As to me – when I was sitting there in the quantum chemistry course listening to Fraga (312) talking about quantum chemistry with his, at that time, heavy Spanish accent ('unbertal' function is what I understood (having just arrived with my own German accent), vs. unperturbed function) - I had come over form Europe with no quantum chemistry training and didn't understand too much of it at first. And then, pretty much from the start, I used your book to overcome my difficulties. How would you explain your didactic feeling?

M: I don't know! But I've always been primarily a teacher, I think. I just thought that research is just a help for teaching. I mean, I could not do a job which is only research, I think {laughs}. I still like teaching, I like seeing students, and trying to say something. It doesn't matter what level, you know.

A: Do you think of your own problems which you had when you went into the field?

M: Well, yes, some of the books I've written because I was teaching a course and I felt I would need to write a book to go with the course. Others, you reach a stage in research where you feel you would like to put it altogether now. And so ... {reflecting} ... I've always been a quick worker, actually, I think, that's a great advantage, it leaves me lots of time to do other things {laughs}. I look at my colleagues and I see they take twice as long to do anything as I take, a very great advantage. So, yes, I used to write a book, I reckon it took two years to write a book, mainly in the evenings {laughs}.

A: Well, the one about the electron spectra that is still being used at the University of Constance, for instance.

M: Yes, is it the German edition? A German translation (313)?

A: Yes.

M: Well, the nice thing is that not much of it is totally stupid. Of course it's 30 years old now, more than 30 years old, but it's not that there is a terrible gap. It is not that it is wholly wrong {laughs}. And I think, that's true of most of the books. If I look at them now. Of course subjects advance but I don't look and say, god, that's terrible, that's really out of date.

A: The basics remain.

M: Yes, you’ve got to know when to write that book, the basics. If you write it too early in the subject then you will get out of date. So you’ve got to know -, even my book "Semiempirical" with Harget, I think, if anybody was coming into the field now, although they wouldn't get the latest techniques they could go to that book and they could say, right, this is obviously what people were doing. They would find the beginnings of Dewar's work in there. They won't find the last bit of Dewar because that was in later generation, but I think you would look at the book and you get the basic ideas out of it.

A: You left out some of the heavier mathematics and that, I think was, when I was a student, the point of its usfulness. Some years ago when I a gave sort of a pre-course into quantum chemistry to some students I again used your book Valence Theory because I felt it is a good entry point for young chemists.

M: You see, I've never written a book on quantum mechanics. It would be very interesting to do. I could think that's a lot of fun. But there are of course a lot of good books on quantum mechanics. When I wrote "Valence" there was nothing beyond Coulson. And Coulson's book, never really - it didn't tell you how to do things very much. I mean, it was a great book {laughs}, a marvellous book, but it stopped at some stage.

We wanted to do something a bit more, taught you the basics but also just sent you a little bit further. We didn't want to spent a lot of time on operators and you know, Hermitian matrices and how to diagonalize them, that wasn't what we tried to do. I mean, I don't know, nobody ever asked {accentuated by M..} me to write a book. Nobody ever came to me and said we need a book on such and such. I think that's the great advantage. I wrote a book because I wanted to write it. And when it was finished I asked if anybody wanted to publish it {laughs}.

A: And then had four edition, isn't it?

M: Yes, it's a great sadness that it's out of print. And you can't get second hand copies they all disapeared somewhere in the world, I don't know where they are. Great sadness {laughs}.

Encountering Coulson

A: Now, can you characterize some of the persons you worked with. Coulson, for example, have you known him?

M: Yes, I knew him very well. A marvellous, gentle man. You know, he was a serious, very serious man of religious beliefs; very kindly, everybody liked him. He had also an excellent brain.

A: Is there any biography out on Coulson.

M: Well, no. There would be an orbituary of the Royal Society. Everybody who is a fellow who dies, gets a nice orbituary {laughs}. There is a nice one on Hückel for example, I think I have a copy somewhere.

A: I think, I know it, written by Longuet-Higgins?

M: Yes, that's nice. So Coulson was a gentle fellow. And given that he was a mathematician and finished his academic career as a professor of mathematics - nevertheless he had this great understanding of chemistry.

A: How did he get into this Hückel field?

M: Well, I think, he went to work with Lennard-Jones. I don't know else how he did it.

Longuet-Higgins - grave illness

A: And Longuet-Higgins?

M: Well, he is not well. I don't think he will receive you. He has been very ill in the past year {1999}, I've been trying to contact him for some time. Yesterday I was making inquiries. So I think, he is not well. He’s spent 30 years doing experimental psychology. Well, I've been told that he's been in hospital with depression. So it will be tough.

A: So, well you told how the atmosphere was at Longuet-Higgins' - , how many research people did he have in the time you were there.

M: Well, he never had many directly doing PhDs with him at that time. The Cambridge group was very big. Salem, you know, the younger generation, Salem was there one stage. He typically had one student a year. That's not much. But he had a large group in chemistry. People came in, lots of visitors came because of his reputation.

A: Is the Cambridge atmosphere, you just mentioned the Oxford atmosphere, is it different?

M: Yes, well Cambridge, I mean everybody would say that the outstanding theoretical chemistry place in the UK is Cambridge, always was and is now. Oxford had a little bit but it never reached the Cambridge level. I don't think it would be any argument about that. Have you talked with Mark Child at Oxford? Child is another student of Longuet-Higgins, he is a professor in Oxford.

A: I'm mainly pursuing semiempirical projects.

M: Child is a little bit different but he was a PhD student of Longuet-Higgins. Longuet-Higgins is a person who had good students. Good people gathered good students, I think, that's the way of it. They don't have to try. Longuet-Higgins had an accumulation of excellent students {laughs}.

Summer Schools by Löwdin as well as others

A: What was in the semiempirical times the effectiveness of Lowdin? Everybody was at Löwdin's place. Was it really effective or was it just a way to do things, you know, to meet there or something.

M: Well, there was a time when the instruction for students in theoretical chemistry was very weak in most places, and there were two schools set up, summer schools, to try and remedy that. One was Löwdin's and the other was Coulson's. And they both used to run summer school and Löwdin a winter school as well eventually. Now, I think, Löwdin, he did some semiempirical work but it was not his prime interest. I mean, he was interested in solids of which there were some semiempirical ideas within that. He was very influential as a school, yes. I never had much to do with him.

A: Have you been there to that school?

M: I've never been to his Swedish school, I've been to the Florida one. But only once.

{Murrell takes a deep breath and sighs, apparently due to the interview.}

A: Most people went there or did the British go more to Coulson's?

M: Well, I think, probably Coulson's school was quite important, but it was still a school for those who were learning the subject. It wasn't so much a school for taking things a lot further. Later on it became a bit like that. The early work was all to try and teach people the basics of quantum mechanics and Hückel theory and things like that. And a lot of people went through that.

We haven't talked about the German's school, I mean, it's a pity not to mention. Because Hückel himself is a very interesting character. I actually have on my desk over there, Hückel's original papers on ethylene and where he does Hückel theory - marvellous papers. But he was a physicist.

The other person who was fairly influencial in Germany was Hartmann. But on the whole during the 1930ies and 1940ies Germany was not very excited by theoretical things. You know, people like Hartmann had real struggle to do it, to be excepted. Now it's changed completely of course.

A: Jug from Hannover had talked about that in an interview with me, interview with me, he was a student of Hartmann’s ... Yet another factor might be the difference in the German, the British or the American university system - - -

M: Well, I mean the big difference is that in Britain and America the young people are allowed the freedom to do things.

Some Remarks Concerning the Work of Roothaan

A: Yes. Another question still: somebody said about Roothaan, 'well, he actually only wrote up the ideas of the Mulliken group'. How would you see that?

M: I'm not aware that Roothaan ever was interested in semiempirical work. The Roothaan group and the Cambridge group were developing a selfconsistent field model. And the Chicago group put it much more into programming. Roothaan, I think, he was essentially a mathematician or you know, mathematical physicist. I don't think he contributed to chemistry particulary.

A: Roothaan's paper was very clearly written. Yet some people maintain that most of Roothaan's work there could be found in those previously published Naval Research reports of the Mulliken group?

M: Well, one of the most heavily used reprints that I ever had was a paper by Mulliken in which he calculated overlap integrals - THE classic: Mulliken, Rieke, Orloff and Orloff (314). And you know, my copy of this paper just got totally disintegrated because in the 1950ies and 1960ies when you didn't have computers at hand, you know, it was just like using log tables. So Mulliken was terribly influential in those days. He was a very special fellow. Mulliken was a very slow man in thinking, so if you asked him a question today, you know, you wouldn't get the answer till tomorrow. And this could be a bit frustrating, I mean. I'd rather have the wrong answer but have it now {laughs hilariously}.

A: That's why he was lost out against Linus Pauling, didn't he?

M: Yes, they were quite different characters, weren't they? But very well respected, of course in the end.

A: And Ruedenberg

M: Yes, Ruedenberg, he was at Chicago when I was there. He did a lot of free electron theory of course. There was a bit of spectroscopy out of it. I look upon him as a more mathematical basis and rather concentrating on mathematical problems.

Parr gets mentioned

A: And then Parr ?

M: Parr, he is a very fine theoretician, very - well, an English style theoretician.

A: Is he English?

M: No, {laughs}, no. But I think, you know, the type of work he did was very much the type of work that was going on in England at the time. A very good man. I knew him quite well, he is a few years older than me. He's probably about 75 now, I imagine.

Kohn and Pople and the Nobel Prize of 1998

A: A side line now. How did or does quantum chemistry here view the Nobel Prize for Pople and Kohn? In Germany there were some implicit second thoughts about Kohn and his obtaining the Nobel Prize.

M: Well, I think, most people were surprised, they would not have anticipated Kohn. But having come out and having known that density functional theory is very influential now then, in retrospect, it wasn't an outrage. But for sheer influence and hard work etc. Pople must be a very influential person. He had the basics there and he influenced an enormous number of people. He had several terribly important ideas.

The underestimation of Boys

A: Did you know Boys. He was a very shy man, wasn't he?

M: He was shy, he was totally self-centred. But he knew the way forward, you know, but we did not appreciate him at the time.

A: Did Longuet-Higgins?

M: No, Longuet-Higgins hated him, yes (laughs), hated the work, simply couldn't abide it {chuckles quite thoughtfully}.

A: Madame Fisher said ab initio is not ab initio, she meant it's still parameterized.

M: Well, I think, I can see it as still ab initio in principle you get it from Schrödinger. But Boys, you see, wrote in 1955 a paper which said this is the way we should do it. And indeed, you know, that's the way it's been done. That was before computers effectively started {laughs}, just incredibly. He calculated the energy of the water molecule on the first computer that was available{chuckles quite thoughtfully}.

A: Why didn't Longuet-Higgins like the work. Was it too numerical?

M: Well, I would think, Boys - - -{reflecting}. Cambridge was an exceedingly agressive place. If you came to give a lecture at Cambridge, you could reckon half the lecturers went away feeling bad {laughs}. Most people are kind to their lecturers, but if Longuet-Higgins thought the work wasn't of the highest quality, you know, he would interupt and he would be say, look, I think, you got it wrong or this is not good enough etc.

A: Still nowadays?

M: Probably, yes, you know, we take the tradition on. But Boys was always a bit diffident and he didn't have experiments at his finger tips and it looked just like a branch of mathematics. And Longuet-Higgins, although he could do mathematics, that wasn't what he was interested in.

A: Was Longuet-Higgins interested in describing the compounds?

M: I don't think Longuet-Higgins was interested in proving that the water molecule was bent, right? I mean, well, his attitude was we know the water molecule is bent. So when you get, you know, lots of calculations which lead to the answer that the water molecule is bent he would say 'so what'.

But of course Frank Boys was looking further ahead, Frank obviously knew so what, he wanted to show that this technique was useful, so when he got on to something that was not obvious it would have some basis. But Longuet-Higgins, I think, never saw that, and the rest of the group was very influenced by Longuet-Higgins. Boys had just a few students, Shavitt was one of them. I don't know, if you have ever met him? Quite an important fellow, but he's not semiempirical.

A: What have I not asked?

M: I don't know. I think, when you say semiempirical methods, I mean, basically what you're saying is probably semiempirical molecular orbital theory.

A: Yes, people like Jug, who started from Hückel, finally developed his SINDO-Method.

M: Yes, absolutely. And that field has been an important field. But certainly the British view is that that is a small part of theoretical chemistry, an interesting part of theoretical chemistry. That, I think, as far I being concerned that has been, what shall I say, one fifth of my accademic career {laughs}.

A: Yes, of course, but my point here is primarily centered around your early work, your great book Valence Theory and of the huge field of activity it has had.

M: {laughs} Well, it is nice of you to say.

A: Professor Murrell - thank you very much for this relaxed and informative interview in direction of the early methods and events.

References and Notes

Some references to related books of Murrell (not exhaustive):

(1) J.N. Murrell, S.F.A. Kettle and J.M. Tedder : Valence Theory. John Wiley & Sons, Ltd, London, 1965.   ->return

(2) J.N. Murrell : Elektronenspektren Organischer Moleküle. Bibliographisches Institut Mannheim, Mannheim, 1963. The original was : The Theory of the Electronic Spectra of Organic Molecules. Menthuen & Co Ltd, London, 1963.   ->return

(3) J.N. Murrell and A.J. Harget: Semi-empirical Self-consistent-field Molecular Orbital Theory of Molecules. Wiley-Interscience, London, 1972.   ->return

(4) J.N. Murrell, S.F.A. Kettle and J.M. Tedder : The Chemical Bond. John Wiley & Sons, Ltd, Chichester, 1985.   ->return

Some references to Murrell's earlier papers (not exhaustive):

(5) J.N. Murrell and C. Longuet-Higgins: The electronic spectra of aromatic molecules. III: The effect of inductive substituents.
Proc. Roy. Soc. (London) 68A, 329-39 (1955).   ->return

(6) C. Longuet-Higgins and J.N. Murrell : The electronic spectra of aromatic molecules. V. The interactions of two conjugated systems.
Proc. Roy. Soc.(London)68A, 601-611 (1955).   ->return

(7) J.N. Murrell The electronic spectra of aromatic molecules. VI. The mesomeric effect.
Proc. Roy. Soc. (London)68A, 969-75 (1955).   ->return

(8) J.N. Murrell and H.C. Longuet-Higgins : Interaction between the aromatic chromophores in polyphenyles.
J. Chem. Soc.(London)1955, 2552-2556.   ->return

(9) J.N. Murrell and J. A. Pople The intensities of the symmetry-forbidden electronic bonds of benzene hydrocarbons.
Proc. Roy. Soc. (London)69A, 245-52 (1956).   ->return

(10) J.N. Murrell Effect of acid on el. spec. of org. mol. contain. conjug. & unconj. N atoms.
J. Chem. Soc. (London)1959, 296-299 (1959).   ->return

(11) J.N. Murrell pi-electron spectra of benzene N-heterocyclics.
J. Mol. Phys.1, 384-390(1958).   ->return

(12) J.N. Murrell and Salem Energy of excited electronic states as calculated with ZDO approx.
J. Chem. Phys.34, 1914 (1961).   ->return

(13) Heilbronner and J.N. Murrell The prediction of the spectra of aromatic hydrocarbons.
J. Chem. Soc. (London)1962, 2611-2615 (1962).   ->return

(14) Heilbronner and J.N. Murrell A theor. study of the el.spec of the benzazul. & benzolog.-trop. cation ...
Mol. Phys. 6, 1-18 (1963).   ->return

(15) Heilbronner and J.N. Murrell Effect of alkyl groups on the electronic spectra of benzenoid hydrocarbons.
Theor. Chim. Acta 1, 235-244(1963).   ->return

(16) J.N. Murrell El. Spect. of subst. arom hydrocarb.
Tetrahedron 19, 277- (1963).   ->return

(17) Heilbronner, Binsch, and J.N. Murrell The theory of double bond fixation in conjugated hydrocarbons.
Mol. Phys.11, 305-320 (1966).   ->return

(18) Heilbronner,Baumann and J.N. Murrell Molecular orbitals and the virial theorem.
Theor. Chim. Acta5, 87-94 (1966).   ->return

(19) Trinajstic, J.N. Murrell and Hincliffe Calculations on the energy levels of alternant hydrocarbon anions.
Trans. Farad. Soc.62, 1362-1369 (1966).   ->return

(20) J.N. Murrell and Silk Opt. atomic orbital exponents for molec. wave functions.
Symp. Farad. Soc.2, 84-94 (1968).   ->return

(21) J.N. Murrell Photoel. spec. correl. of MO of methane, eth.,prop.,isobut & neopent.
Trans. Farad. Soc. 68 , 1709-1718 (1972).   ->return

(22) J.N. Murrell The many-body expan. of the pot en. func. for elemental clusters.
Int. J. Quant. Chem. 37 , 95-102 (1990).   ->return

(23) J.N. Murrell Semi-empirical electronic structure models.
J. Mol. Struct. THEOCHEM 424, 93-99 (1998).   ->return

Some references to Murrell's later publications (not exhaustive):

(24) S. Li, R.L. Johnston and J.N. Murrell, Cluster structures and stabilities from solid state potentials
J. Chem. Soc., Faraday Trans.,88,1229-1236 (1992).   ->return

(25) J.N. Murrell Potential energy functions for atomic solids
Chemické listy,85,769-775 (1991).   ->return

(26) J.N. Murrell and S D Bosanac The Theory of Atomic and Molecular Collisions
Chem. Soc. Revs.,1992,17-28.   ->return

(27) B R Eggen, R L Johnston, S Li and J N Murrell Potential energy functions for atomic solids IV reproducing the properties of more than one solid phase
Mol.Phys.76, 619-633 1992).   ->return

(28) X Liu and J N Murrell Analytical potential for HCP from spectroscopic data
J.Chem. Soc., Faraday Trans.,88,1503-1506 (1992).   ->return

(29) J C Belchoir, J N Murrell and S D Bosanac The hardness factor in rotational inelastic scattering
Mol. Phys.,77,727-733 (1992).   ->return

(30) L J Dunne and J N Murrell Symmetry in the superconducting, insulating and metallic phases of doped cuprates
Physica C,196,185-190 (1992).   ->return

(31) J-Y Fang, R L Johnston and J N Murrell Potential energy functions for atomic solids v. application to alkali metal solids
Mol. Phys.,78,1405-1422 (1993).   ->return

(32) J-Y Fang, R L Johnston and J N Murrell Potential energy functions for Cu, Ag and Au solids and their application to clusters of these elements
J. Chem. Soc., Faraday Trans., 89,1659-1665()1993.   ->return

(33) J C Belchior, J N Murrell and S D Bosanac A hard shape potential model for atom-symmetric top inelastic cross sections
Chem. Phys., 176,155-164 (1993).   ->return

(34) R L Johnston, P J Knowles and J N Murrell : Molecular Orbital Theory.
Royal Society of Chemistry, Annual Reports C ,(1988).   ->return

(35) F Gao, R L Johnston and J N Murrell Empirical Many-Body Potential Energy Functions for Iron
J. Phys. Chem., 97,12073-12082(1993).   ->return

(36) K M Andersson, R L Johnston and J N Murrell Empirical potential-energy function for calcium solids and clusters
Phys. Rev. B, 49,3089-3097(1994).   ->return

(37) J Uppenbrink, R L Johnston and J N Murrell Modelling transition metal surfaces with empirical potentials
Surface Science,304,223-236 (1994).   ->return

(38) B R Eggen, A J Marks, J N Murrell and S C Farantos Water clusters - a speculation
Chem. Phys. Letts., 219,247-251(1994).   ->return

(39) J C Belchior and J N Murrell An inversion procedure from rotational total cross sections
J. Chem. Phys., 101,2016-2022(1994).   ->return

(40) B R Eggen, R L Johnston and J N Murrell Carbon cluster structures and stabilities predicted from solid-state potentials
J. Chem. Soc. Faraday Trans.,90,3029-3037(1994).   ->return

(41) F Y Naumkin, P J Knowles, J N Murrell Towards reliable modelling of large clusters: on the overall accuracy of the diatomics-in-molecule method for rare gas cluster ions
Chem. Phys., 193,27-36(1995).   ->return

(42) P J Knowles and J N Murrell The metastable quartet state of He4+
Letters to the Editor, Communications, J. Chem. Phys., 102,9442-9443(1995).   ->return

(43) P J Knowles, J N Murrell and E J Hodge An n-valued representation of Hen+ potentials
Mol. Phys., 85,243-255(1995).   ->return

(44) J N Murrell Towards a general strategy for global interatomic potentials for elemental solids, surfaces and clusters
Philosophical Magazine B, 73,163-174(1996).   ->return

(45) J E Hearn, R L Johnston, S Leoni and J N Murrell Global potentials for calcium and strontium solids
J. Chem. Soc., Faraday Trans., 92,425-432(1996).   ->return

(46) P J Knowles and J N Murrell The structures and stabilities of helium cluster ions
Mol. Phys., 87,827-833(1996).   ->return

(47) S D Bosanac and J N Murrell Collision dynamics for small helium cluster ions
Chem. Phys. Letts., 254,69-72(1996).   ->return

(48) M J Cohen and J N Murrell An analytic function for the three-body potential of He3
Chem. Phys. Letts., 260,371-376(1996).   ->return

(49) L J Dunne, J N Murrell and E J Brändas Off-diagonal long-range order, ?- pairing, and Friedel oscillations in high Tc cuprate superconductors and the ground state of the extended Hubbard model
International Journal of Quantum Chemistry, 63,675-684(1997).   ->return

(50) J Hernandez-Cobos, I G Kaplan and J N Murrell An analytical representation of the model potential for beryllium trimers
Mol. Phys., 92,63-69(1997).   ->return

(51) H Cox, R L Johnston and J N Murrell Modelling of surface relaxation and melting of aluminium
Surface Science, 373,67-84(1997).   ->return

(52) B R Eggen, J N Murrell and L J Dunne Hydrogen - The first alkali metal?
Solid State Communications, 105,119-123(1998).   ->return

(53) J N Murrell Semi-empirical electronic structure methods
Journal of Molecular Structure (Theochem), 424, 93-99(1998).   ->return

(54) H Cox, X Liu and J N Murrell Modelling Cu, Ag and Au surfaces using empirical potentials
Mol. Phys., 93, 921-924(1998).   ->return

(55) S D Bosanac, and J N Murrell Unimolecular dissociation dynamics of helium cluster ions
Chem. Phys. Letts., 291,64-70 (1998).   ->return

(56) L J Dunne, E J Brändas, J N Murrell and V Coropceanu Group theoretical identification of active localized orbital space in high Tc cuprate superconductors
Solid State Communications,108,619-623(1998).   ->return

(57) J N Murrell Michael James Steuart Dewar 24 September 1918 - 11 October 1997
Biog, Mems, Fell. R. Soc. Lond., 44,127-140 (1998).   ->return

(58) L.J.Dunne, E.J.Brandas, and J.N.Murrell D-Wave Condensate and Essential Phenomenological Description of some Properties of High Tc Cuprate superconductors.
Int.J.Quant.Chem., 74617-626,(1999).   ->return

(59) H.Cox, R.L.Johnston, and J.N.Murrell Empirical Potentials for Modelling Solids, Surfaces, and Clusters
J.Solid State Chem., 145,517-540(1999).   ->return

(60) J.N.Murrell Bonding and the Theory of Atoms and Molecules
ch.2, The New Chemistry, Ed. Nina Hall,,(2000),32-42, C.U.P..   ->return

(61) J.N.Murrell, F.Y.Naumkin, and C.R.Griffiths The Structures and Stabilities of Mixed Inert Gas Cluster Ions: NeHen+ and ArHen+
Mol. Phys., 99, 115-132 (2001).   ->return

(62) E.J.Brandas, L.J.Dunne, and J.N.Murrell Phenomenological Description of D-Wave Condensates in High-Tc Superconducting Cuprates. in :
New Trends in Quantum Systems in Chemistry and Physics, eds. J.Maruani et al., ,(2000), 2.289-304.   ->return

(63) L.J.Dunne, J.N.Murrell, and P.Jemmer
Chem.Phys.Letts., 336 ,1-6(2001).   ->return

(64) J.N.Murrell
Helv.Chim.Acta, 84 ,1314-1327(2001).   ->return

Some references concerning Lennard-Jones (not exhaustive):

(65) J.E. Lennard-Jones "(formerly J.E. Jones)" and P.A. Taylor: Some theoretical calculations of the physical properties of certain crystals.
Proc. Roy. Soc. (London) 109A, 476-508 (1925).   ->return

(66) J.E. Lennard-Jones : The forces between atoms and ions.
Pro. Roy. Soc. (London) 109A,584-597 (1925).   ->return

(67) J.E. Lennard-Jones: Molecular fields of hydrogen, nitrogen and neon.
Pro. Roy. Soc. (London) 112A,214-229(1926).   ->return

(68) J.E. Lennard-Jones and B.M. Dent : The forces between atoms and ions.
Pro. Roy. Soc. (London) 112A,230-234 (1926).   ->return

(69) J.E. Lennard-Jones : The pressure of gaseous mixtures.
Nature 119,459 (1927).   ->return

(70) J.E. Lennard-Jones: electronic structure of some diatomic molecules.
Trans. Farad. Soc. 25, 668 (1929).   ->return

(71) J.E. Lennard-Jones: The Electronic Structure of Some Polyenes and Aromatic Molecules. I - The Nature of the Links by the Method of Molecular Orbitals.
Proc. Roy. Soc [London] A158, 280-296 (1937).   ->return

(72) J.E. Lennard-Jones: The Electronic Structure of Some Polyenes and Aromatic Molecules. II - The Nature of the Links of some Aromatic Molecules.
Proc. Roy. Soc [London] A158, 297-305 (1937).   ->return

(73) J.E. Lennard-Jones, C.A. Coulson: The structure & energies of some hydrocarbon molecules.
Trans. Farad. Soc. 35, 811-823 (1939).   ->return

(74) J.E. Lennard-Jones: MO theor. of chem. val I.: the determination of molecular orbitasl. (EBO).
Proc. Roy. Soc. (L.) 198, 1-13 (49).   ->return

(75) J.E. Lennard-Jones: MO theor. of chem. val. II.: Equivalent orbitals in molecules of known sym.(EBO).
Proc. Roy. Soc. (L.) A198, 14-26 (49).   ->return

(76) G.G. Hall, J.E. Lennard-Jones: MO theor. of chem. val. III.: properties of molecular orbitals. (EBO).
Proc. Roy. Soc. (L.) A202, 155-165 (50).   ->return

(77) J.E. Lennard-Jones, J. Pople: MO theor. of chem. val. IV.: the significance of equivalent orbitals (EBO).
Proc. Roy. Soc. (L.) A202, 166-180 (50).   ->return

(78) G.G.Hall, J.E. Lennard-Jones: MO theor. chem. val. VII.: mol. struc. in terms of equivalent orbitals (EBO).
Proc. Roy. Soc. (L.) A205, 357-374 (51).   ->return

(79) J.E. Lennard-Jones, J.Pople: Survey of princ. det. struc...mol. I.: factors resp. mol. shape & bond energies.
Disc. Farad. Soc. 10, 9-18 (51).   ->return

(80) J.E. Lennard-Jones, J.Hall: Survey of princ. struc. det. mol. II.: the ioniz. pot & reson. ener.of hydrocarb
Disc. Farad. Soc. 10, 18-27 (51).   ->return

(81) J.E. Lennard-Jones, J.Hall: The ionization of paraffin molecules.
Trans. Farad. Soc. 48, 581-584 (52).   ->return


Some publications of C.A. Coulson (not exhaustive):

(131) J.E. Lennard-Jones, C.A. Coulson : The structure & energies of some hydrocarbon molecules.
Trans. Farad. Soc. 35 , 811-823 (1939).   ->return

(132) C.A. Coulson, H.C. Longuet-Higgins : ??
Rev. Sci. Inst. 85 , 929 (1947).   ->return

(133) H.C. Longuet-Higgins, C.A. Coulson : Theoretical Investigation of the distribution of electrons in some heterocyclic molecules containing nitrogen.
Trans. Farad. Soc. 43 , 87-94 (1947).   ->return

(134) C.A. Coulson, H.C. Longuet-Higgins : Electronic theory of conjugated systems I : general theory.
Proc. Roy. Soc. (L.) A191 , 39-60 (1947).   ->return

(135) C.A. Coulson, H.C. Longuet-Higgins : Electronic theory of conjugated systems II : The ionization of paraffin molecules.
Proc. Roy. Soc. (L.) A192 , 16 (1952).   ->return

(136) C.A. Coulson, H.C. Longuet-Higgins : Electronic theory of conjugated systems III : Bond orders in unsaturated molecules.
Proc. Roy. Soc. (L.) A193 , 447(1948).   ->return

(137) C.A. Coulson, H.C. Longuet-Higgins : Electronic theory of conjugated systems IV : Force constants and interaction constants in unsaturated molecules.
Proc. Roy. Soc. (L.) A193 , 456 (1948).   ->return

(138) C.A. Coulson, H.C. Longuet-Higgins : Electronic theory of conjugated systems V : Interaction of 2 conjugated systems.
Proc. Roy. Soc. (L.) A195 , 188 (1948).   ->return


Some early publications of C.H. Longuet-Higgins (not exhaustive):

(181) C.A. Coulson, H.C. Longuet-Higgins : Electronic theory of conjugated systems I : general theory.
Proc. Roy. Soc. (L.)A191, 39-60 (1947).   ->return

(182) C.A. Coulson, H.C. Longuet-Higgins : Electronic theory of conjugated systems II : The ionization of paraffin molecules.
Proc. Roy. Soc. (L.)A192, 16 (1952).   ->return

(183) C.A. Coulson, H.C. Longuet-Higgins : ??
Rev. Sci. Inst.85,929 (1947).   ->return

(184) H.C. Longuet-Higgins, C.A. Coulson : Theoretical Investigation of the distribution of electrons in some heterocyclic molecules containing nitrogen.
Trans. Farad. Soc. 43 , 87-94 (1947).   ->return

(185) C.A. Coulson, H.C. Longuet-Higgins : Electronic theory of conjugated systems III : Bond orders in unsaturated molecules.
Proc. Roy. Soc. (L.)A193 , 447(1948).   ->return

(186) C.A. Coulson, H.C. Longuet-Higgins : Electronic theory of conjugated systems IV : Force constants and interaction constants in unsaturated molecules.
Proc. Roy. Soc. (L.)A193 , 456 (1948).   ->return

(187) C.A. Coulson, H.C. Longuet-Higgins : Electronic theory of conjugated systems V : Interaction of 2 conjugated systems.
Proc. Roy. Soc. (L.)A195 , 188 (1948).   ->return

(188) H.C. Longuet-Higgins, C.A. Coulson : Theoretical Investigation of the distribution of electrons in some heterocyclic molecules containing nitrogen.
Trans. Farad. Soc. 43 , 87-94 (1947).   ->return

(189) H.C. Longuet-Higgins : The electronic structure of thiophene & related molecules.
Trans. Farad. Soc. 45 , 173-179 (1949).   ->return

(190) H.C. Longuet-Higgins, C.A. Coulson : El. struc. some aza-deriv. of naphthalene, anthracene & phenantrene.
J. Chem. Soc. (Lond)1949, 971-980.   ->return

(191) H.C. Longuet-Higgins, C.A. Coulson : Theoretical investigation electron distrib in heterocyclic ...
Trans. Farad. Soc.43,87 (1949).   ->return

(192) H.C. Longuet-Higgins Studies in MO theory. I.: resonance stud. & MO in unsaturated ...
J. Chem. Phys. 18 , 265-274 (1950).   ->return

(194) H.C. Longuet-Higgins Studies in MO theory. II: ionisation constants of heteroatomic amines.
J. Chem. Phys. 18 , 275-282 (1950).   ->return

(194) H.C. Longuet-Higgins Studies in MO theory. III: substituted aromatics & hetero...
J. Chem. Phys. 18 , 283-291 (1950).   ->return

(195) H.C. Longuet-Higgins Recent developments in molecular orbital theory.
Adv. Chem. Phys.1, 239-265 (1958).   ->return

(196) H.C. Longuet-Higgins, Salem The alternation of bond lenths in long conjugated chain molecules.
Proc. Roy. Soc. (L.)A251, 172-185 (1959).   ->return

(196) H.C. Longuet-Higgins, Salem Altern. bond length on large conj mol. III.: cyclic polyenes C18H18...C30H30
Proc. Proy. Soc (L.)A 257,445-456 (1960).   ->return

(197) H.C. Longuet-Higgins Second quant. in the electr. theor. of mol. in : Lowdin, Quant. Theory of ...
Academic Press, 1966, p.105-122.   ->return

(198) Longuet-Higgins, Wheland Theories of valence.
, (1950).   ->return


Some publications in direction Pariser - Parr (not exhaustive) :

Pariser-Parr : The semiempirical Pariser-Parr PP, also called Pariser-Parr-Pople, PPP, method. It was developed by Pariser and Parr in the US, simultaneously in England by Pople. NOTE : This will be discussed under Parr in this context due to appear at this website in the last months of 2001. (251) R.S. Mulliken and R.G. Parr : LCAO molecular orbital computation of resonance energies of benzene and butadiene, with general analysis of theoretical versus thermochemical resonance energies.
J. Chem. Phys. 19 , 1271-1273 (1951).   ->return

(252) R.G. Parr : On LCAO molecular orbital schemes and theoretical resonance energies.
J. Chem. Phys. 19 , 799-800 (1951).   ->return

(252b) R.G. Parr : A method for estimating electronic repulsion integrals over LCAO MO's in complex unsaturated molecules.
J. Chem. Phys. 20 , 1499 (1952).   ->return

(253) R. Pariser and R.G. Parr : A semi-empirical theory of the electronic spectra and electronic structure of complex unsaturated molecules. I.
J. Chem. Phys. 21 ,466-471 (1953).   ->return

(254) R. Pariser and R.G. Parr : A semi-empirical theory of the electronic spectra and electronic structure of complex unsaturated molecules. II.
J. Chem. Phys. 21 ,767-776 (1953).   ->return

(255) R. Pariser : An improvement of the pi-electron approximation in LCAO-MO theory.
J. Chem. Phys. 21 ,568-569 (1953).   ->return

(256) R.G. Parr and R. Pariser : On the electronic structure and electronic spectra of ethylene-like molecules.
J. Chem. Phys. 23 ,711-725 (1955).   ->return

(257) R. Pariser : Theory of the electronic spectra and structure of the polyacenes and of alternant hydrocarbons.
J. Chem. Phys. 24 ,250-268 (1956).   ->return

(258) R. Pariser : Electronic spectrum and structure of azulene.
J. Chem. Phys. 25 ,1112-1116 (1956).   ->return


Other references :

(281) M.J.S. Dewar and H.C. Longuet-Higgins :
Proc. Roy. Soc. [London] A214 , 482 (1952).   ->return

(281b) M.J.S. Dewar and H.C. Longuet-Higgins : The electronic spectra of aromatic molecules. I. Benzenoid hydrocarbons.
Proc. Phys. Soc. [London] A67 , 795-804 (1954).   ->return

(282) H.C. Longuet-Higgins, J. Pople : The electronic spectra of aromatic molecules. IV.: {exc. sta. odd-altern. hydrocarb. rad. & ions}.
Proc. Phys. Soc. (L.) A 68 , 591-600 (1955).   ->return

(283) G.G. Hall The bond orders of alternant hydrocarbon molecules.
Proc. Roy. Soc. (L.)A 229, 251-259 (1955).   ->return

(284) H.C. Longuet-Higgins, Herzberg Intersection of potential energy surfaces in polyatomic molecules.
Disc. Farad. Soc. 35,77-82 (1963).   ->return

(285) H.C. Longuet-Higgins, L.E. Orgel The poss. exist. of trans. met. compl. of cyclo-butadiene.
J. Chem. Soc. (Lond.) 1956 , 1969-1972 (1956).   ->return

(286) L.E. Orgel An Introduction to Transition-Metal Ligand-Field Theory.
Methuen, London, 1960 and 1967 (2. ed.), John Wiley, New York, 1967.   ->return

(287) {I.'s note : to do that nowadays in a few seconds, just click here.   ->return

(288) Platt, Klevens Spectral resemblances in cata-condensed hydrocarbons.
J. Chem. Phys. 17 , 470-480 (1949).   ->return

(289) Platt, Mann, Klevens Spectral resemblances in azulene & naphthalene.
J. Chem. Phys., 481-484 (1949).   ->return

(290) Platt Classific. of cata-condensed hydrocarbons.
J. Chem. Phys.17, 484-495 (1949).   ->return

(291) Platt, Klevens Spectral resemblances of cata-condensed hydrocarb. Reply to Erich Clar.
J. Chem. Phys.17, 742L (1949).   ->return

(292) H.C. Longuet-Higgins, Rector, Platt : MO calc. on porphine & tetrahydro-porphine.
J. Chem. Phys. 18 , 1174-1181 (1950).   ->return

(293) J.S. Griffith : The Theory of Transition-Metal Ions.
Cambridge, University Press, 1971.   ->return

(294) Boys : Electronic Wavefunctions:

I. A General Method. Proc. Roy. Soc. L. A 200, 542 (1950).

II. Proc. Roy. Soc. L. A 201, 125 (1950).

III. Proc. Roy. Soc. L. A 206, 489 (1951).

IV. Proc. Roy. Soc. L. A 207, 181 (1951).

V. Proc. Roy. Soc. L. A 207, 197 (1951).

VI. Phil. Trans. Roy. Soc. L. 245, 95 (1952).

VII. Phil. Trans. Roy. Soc. L. 245, 116 (1952).

VIII. Phil. Trans. Roy. Soc. L. 245, 139 (1952).

IX. Proc. Roy. Soc. L. A 217, 136 (1952).

X. Proc. Roy. Soc. L. A 217, 235 (1952).

XI. Phil. Trans. Roy. Soc. L. 246, 451 (1954).

XII. Phil. Trans. Roy. Soc. L. 246, 463 (1954).


(295) D.B. Cook : ab initio Valence Calculations in Chemistry.
Butterworth, London, 1974.   ->return

(296) D.B. Cook : Structures and Approximations for Electrons in Molecules.
Ellis Horwood, Chichester, 1978.   ->return

(297) D.B. Cook : Handbook of Computational Chemistry.
Oxford University Press, Oxford, 1998.   ->return

(298) A. Hinchliff : ab initio Determination of Molecular Properties.
Adam Hilger, Bristol, 1987.   ->return

(299a) A. Hinchliff : Computational Quantum Chemistry.
John Wiley and Sons, Chichester, 1989.   ->return

(299b) A. Hinchliff : Modelling Molecular Structures.
John Wiley and Sons, Chichester, 1996.   ->return

(300) N. Trinastic : Molekularne orbitale u kemiji.
Skolska knijga, Zagreb, 1974.   ->return

(301) A. Graovac, I. Gutman, and N. Trinastic : Topological Approach to the Chemistry of Conjugated Molecules.
Springer Verlag, Berlin, 1977.   ->return

(302) N. Trinastic : Chemical Graph Theory, Vol's I and II
Chemical Rubber Company (CRC) Press, Boca Raton, Florida, 1983.   ->return

(303) N. Trinastic : Chemical Graph Theory, Vol's I and II 2nd Ed.
Chemical Rubber Company (CRC) Press, Boca Raton, Florida, 1992.   ->return

(304) N. Trinastic, S. Nikolic, J.V. Knop, W.R. Müller and K. Szymanski : Computational CHemical Graph Theory: Characterization, Enumeration and Generation of Chemical Structures by Computer Methods.
Simon & Schuster/Horwood, Chichester, 1991.   ->return

(305) Milan Randic was prof. at Drake University, Des Moines, Iowa, USA., and simultaneously at Ljubljana. I did not find him on Drake faculty as of Oct. 2001. Does anybody know anything about him? Please send me an e-mail. He has had publications from 1955 on. Probabaly retired.   ->return

(306) D. Lindley : The End of Physics. Myth of a Unified Theory. BasicBooks, New York, 1993. D. Lindley : Das Ende der Physik.
Birkhäuser Verlag, Basel, CH, 1993.   ->return

(307a) B. Vidal : Chimie Quantique.
Masson, Paris, 1993.   ->return

(307b) B. Vidal : Quantique moléculaire.
Londres, New York, 1997.   ->return

(308) M.J.S. Dewar : A Semiempirical Life.
American Chemical Society, Washington DC, 1992.   ->return

(309) Moffitt : Term values in hybrid states.
Proc. Roy. Soc. (L.) A202, 534-547 (1950).   ->return

(310) Moffitt : Aspects of hybridisation.
Proc. Roy. Soc. (L.)A202, 548-564 (1950).   ->return

(311) Moffitt : conjugation in sulfones.
Trans. Farad. Soc.47, 7-15 (1950).   ->return

(312) PS: Fraga wrote many books. Here I quote only one :
S. Fraga : Computational Chemistry.
Elsevier, Amsterdam, 1992.   ->return

(313) J.N. Murrell : Elektronenspektren organischer Moleküle.
Bibliographisches Institut, Mannheim, 1963.   ->return

(314) Mulliken, Rieke, Orloff and Orloff : formulas & numerical tables for overlap integrals.
J. Chem. Phys. 17 , 1248 (1949).   ->return

(315) Matsen MO theory & spec. mono subst of benzene. I & II.
Annual Rev. Phys. Chem. 1, 133-150 (1950).
J. Amer. Chem. Soc. 72, 5243 (1950).   ->return

(xxx). -->

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