Methods in Computational Chemistry: Volume 1 Electron Correlation in Atoms and Molecules PDF
Preview Methods in Computational Chemistry: Volume 1 Electron Correlation in Atoms and Molecules
Methods in Computational Chemistry Volume 1 Electron Correlation in Atoms and Molecules METHODS IN COMPUTATIONAL CHEMISTRY Volume 1 Electron Correlation in Atoms and Molecules Edited by Stephen Wilson A Continuation Order Plan is available for this series. A continuation order will bring delivery of each new volume immediately upon publication. Volumes are billed only upon actual shipment. For further informa tion please contact the publisher. Methods in Cotnputational Chetnistry Volume 1 Electron Correlation in Atoms and Molecules Edited by STEPHEN WILSON University of Manchester Regional Computer Centre Manchester, England Springer Science+Business Media, LLC Library of Congress Cataloging in Publication Data Methods in computational chemistry. Includes bibliographies and index. Contents: v. 1. Electron correlation in atoms and molecules / edited by Stephen Wilson. 1. Chemistry —Data processing. I. Wilson, S. (Stephen), 1950- OD39.3.E46M47 1987 542 87-7249 ISBN 978-1-4899-1985-4 ISBN 978-1-4899-1985-4 ISBN 978-1-4899-1983-0 (eBook) DOI 10.1007/978-1-4899-1983-0 © 1987 Springer Science+Business Media New York Originally published by Plenum Press, New York in 1987 Softcover reprint of the hardcover 1st edition 1987 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher Contributors Ivan Cernusak, Department of Physical Chemistry, Comenius University, Bratislava, Czechoslovakia Karol Jankowski, Institute of Physics, Nicholas Copernicus University, Toruil, Poland Vladimir Kello, Department of Physical Chemistry, Comenius University, Bratislava, Czechoslovakia Jozef Noga, Institute of Inorganic Chemistry, Center for Chemical Research, Slovak Academy of Sciences, Bratislava, Czechoslovakia Miroslav Urban, Department of Physical Chemistry, Comenius Univer sity, Bratislava, Czechoslovakia B. H. Wells, Physical Chemistry Laboratory, University of Oxford, Oxford, England s. Wilson, University of Manchester Regional Computer Centre, Manchester, England v Foreword When, forty years ago, as a student of Charles Coulson in Oxford I began work in theoretical chemistry, I was provided with a Brunsviga calculator-a small mechanical device with a handle for propulsion, metal levers for setting the numbers, and a bell that rang to indicate overflow. What has since come to be known as computational chemistry was just beginning. There followed a long period in which the fundamental theory of the "golden age" (1925-1935) was extended and refined and in which the dreams of the early practitioners were gradually turned into hard arithmetic reality. As a still-computing survivor from the early postwar days now enjoying the benefits of unbelievably improved hardware, I am glad to contribute a foreword to this series and to have the opportunity of providing a little historical perspective. After the Brunsviga came the electromechanical machines of the late 1940s and early 1950s, and a great reduction in the burden of calculating molecular wavefunctions. We were now happy. At least for systems con taining a few electrons it was possible to make fully ab initio calculations, even though semiempirical models remained indispensable for most molecules of everyday interest. The 1950 papers of Hall and of Roothaan represented an important milestone along the road to larger-scale non empirical calculations, extending the prewar work of Hartree and Fock from many-electron atoms to many-electron molecules-and thus into "real chemistry." But in a practical sense perhaps the most dramatic ~vent was the appearance of the automatic digital computer-which ended an era and opened a new one. The first electronic computer I used was the "Whirlwind" at MIT in 1954; it solved my large (20 x 201) systems of secular equations in only a few minutes, but high-level languages were not then available and "integral packages" were nonexistent. Integrals over Slater orbitals were evaluated using Barnett-Coulson expansion techniques (and desk machines) and a single three-center two-electron integral might take a few hours of tedious vii viii Foreword work. Merely computing the integrals in readiness for a "double-zeta" calculation on the ammonia molecule (today within the reach of a personal computer) would have taken about fifteen working years so we had to be less ambitious. Nowadays, ab initio calculations of near-Hartree-Fock accuracy, even on quite large molecules, are regarded as "standard"; freely available program packages have brought the application of sophisticated theories within the reach of any chemist with access to (in today's terms) quite modest computing power. And whereas thirty years ago the predictions of theoretical chemists were greeted with, at best, skepticism or, at worst, derision, there is now a danger that chemists with computers put too much trust in their numerical results; for the magic words "ab initio" do not confer some kind of guarantee that the output from a computer will be significant, and programs are frequently used in situations quite outside their range of applicability. Unless computing power is applied with discrimination and understanding even the most elaborate calculations can easily lead to nonsense. There is a more fundamental problem in the interpretation of numerical results and in the assessment of their true significance, one with which the first volume in the series is concerned: the "correlation error," which remains even when a total electronic energy is computed at the Hartree-Fock limit, may well be a thousand times greater than the required barrier height or dissociation energy-so how can reliable predic tions of anything be made? Many of the real innovations of theory in recent years have to do with this so-called "correlation problem" but the details are mathematically and conceptually demanding and are buried in a vast literature. Techniques for removing the correlation error have not yet been embodied in "standard" programs that can be used by the uninitiated. Those which do exist make increasingly heavy demands on the user-he will need a considerable appreciation of the limitations and characteristics of the underlying theories; he will have to make intelligent choices of input data and control parameters and to know something of the algorithms used along the route from input to output; he will have to know what questions it is reasonable to ask and how to interpret the "answers" which emerge. The appearance of this series-which aims at bringing advances in theory, and especially their computational implementation, within the reach of chemists who need to make calculations, whether on molecular structure and behavior, on reaction dynamics, or on the bulk properties of chemical systems-is timely and to be welcomed. As the subject of its first volume, the choice of electron correlation in atoms and molecules-a topic which has haunted quantum chemistry for many years and is now the sub ject of massive computational effort-is particularly appropriate. This book Foreword ix is the work of experts, who write with authority and clarity on their chosen fields, and forms a fitting start to the series. I wish it, and the volumes that will follow, every success. Roy McWeeny Department of Chemistry University of Pisa Pisa, Italy Preface Today the digital computer is a major tool of research in chemistry and the chemical sciences. However, although computers have been employed in chemical research since their very inception, it is only in the past ten or fifteen years that computational chemistry has emerged as a field of research in its own right. The computer has become an increasingly valuable source of chemical information, one which can complement and sometimes replace more traditional laboratory experiments. The com putational approach to chemical problems can not only provide a route to information which is not available from laboratory experiments but can also afford additional insight into the problem being studied, and, as it is often more efficient than the alternatives, the computational approach can be justified in terms of economics. The applications of computers in chemistry are manifold. A broad overview of both the methods of computational chemistry and their applications in both the industrial research laboratory and the academic research environment is given in my book Chemistry by Computer (Plenum Press, 1986). Applications of the techniques of computational chemistry transcend the traditional divisions of chemistry-physical, inorganic, and organic-and include many neighboring areas in physics, biochemistry, and biology. Numerous applications have been reported in fields as diverse as solid-state physics and pesticide research, catalysis and pharmaceuticals, nuclear physics and forestry, interstellar chemistry and molecular biology, surface physics and molecular electronics. The range of applications con tinues to increase as research workers in chemistry and allied fields identify problems to which the methods of computational chemistry can be applied. The techniques employed by the computational chemist depend on the size of the system being investigated, the property or range of properties which are of interest, and the accuracy to which these properties must be measured. The methods of computational chemistry range from quantum mechanical studies of the electronic structure of small molecules to the xi
The list of books you might like
