Ab Initio Valence Calculations in Chemistry


Book Description

Ab Initio Valence Calculations in Chemistry describes the theory and practice of ab initio valence calculations in chemistry and applies the ideas to a specific example, linear BeH2. Topics covered include the Schrödinger equation and the orbital approximation to atomic orbitals; molecular orbital and valence bond methods; practical molecular wave functions; and molecular integrals. Open shell systems, molecular symmetry, and localized descriptions of electronic structure are also discussed. This book is comprised of 13 chapters and begins by introducing the reader to the use of the Schrödinger equation to solve the electronic structure of molecular systems. This discussion is followed by two chapters that describe the chemical and mathematical nature of orbital theories in quantum chemistry. Two general ways of using chemical and physical information in looking for approximate solutions of the Schrödinger equation are highlighted: model approximations and numerical approximations. Attention then turns to atomic orbitals as the basis of a description of molecular electronic structure; practical molecular wave functions; and a general strategy for performing molecular valence calculations. The final chapter examines the nature of the valence electronic structure by using invariance with respect to transformations among the occupied molecular orbitals and among the atomic orbitals. This text will be of interest to students and practitioners of chemistry, biochemistry, and quantum mechanics.







Ab Initio Calculations


Book Description

Until recently quantum chemical ab initio calculations were re stricted to atoms and very small molecules. As late as in 1960 Allen l and Karo stated : "Almost all of our ab initio experience derives from diatomic LCAO calculations ••• N and we have found in the litera ture "approximately eighty calculations, three-fourths of which are for diatomic molecules ••• There are approximately twenty ab initio calculations for molecules with more than two atoms, but there is a decided dividing line between the existing diatomic and polyatomic wave functions. Confidence in the satisfactory evaluation of the many -center two-electron integrals is very much less than for the diatom ic case". Among the noted twenty calculations, SiH was the largest 4 molecule treated. In most cases a minimal basis set was used and the many-center two-electron integrals were calculated in an approximate way. Under these circumstances the ab initio calculations could hard ly provide useful chemical information. It is therefore no wonder that the dominating role in the field of chemical applications was played by semiempirical and empirical methods. The situation changed essentially in the next decade. The problem of many-center integrals was solved, efficient and sophisticated computer programs were devel oped, basis sets suitable for a given type of problem were suggested, and, meanwhile, a considerable amount of results has been accumulated which serve as a valuable comparative material. The progress was of course inseparable from the development and availability of computers.




Valence Bond Methods


Book Description

Publisher Description




AB Initio Calculation of the Structures and Properties of Molecules


Book Description

This book is intended as a guide to the ab initio calculation of molecular structure and properties. It provides the necessary working information to enable the non-specialist to use and understand electronic structure methods and related computing technology, despite the high level of sophistication of quantum chemical methods. The initial chapters define and outline theoretical concepts, methods and computational approaches. Descriptive information and definitions of the terminology are given first; more detailed and mathematical explanations follow. These first chapters thus provide the background information needed to use the extensive literature of ab initio electronic structure theory. The next chapter first provides an overview of the technical issues relating to molecular properties, and then gives a rather detailed but general development. The latter part of this chapter is mainly intended for those first encountering the methodologies of properties determination and intending to pursue further developments. The other chapters provide reviews of calculations in the literature and assessments of factors influencing accuracy. The book is particularly useful to those who need a working understanding of ab initio calculations and well-suited to graduate students and researchers in computational and theoretical chemistry, researchers in electronic structure, spectroscopists and organic chemists.




Diatomic Molecules


Book Description

Diatomic Molecules: Results of Ab Initio Calculations provides the results obtained from quantum-mechanical calculations on the electronic structure of diatomic molecules. This six-chapter text also discusses the related concepts of ab initio calculation methods. This book considers first the primary methods used in the computation of molecular wave functions and of related properties. This topic is followed by discussions on the linear combination of atomic orbital and linear combination of mixed atomic orbital approximations and basis sets; electronic population analysis; spectroscopic transition probabilities; and the nature of chemical bonding. The remaining chapters examine the features of various theories that become prominent when two or more electrons are present, or are important in hydrides or homopolar and heteropolar molecules. This text will be of great value to organic and inorganic chemists and physicists.




Theory and Applications of the Empirical Valence Bond Approach


Book Description

A comprehensive overview of current empirical valence bond (EVB) theory and applications, one of the most powerful tools for studying chemical processes in the condensed phase and in enzymes. Discusses the application of EVB models to a broad range of molecular systems of chemical and biological interest, including reaction dynamics, design of artificial catalysts, and the study of complex biological problems Edited by a rising star in the field of computational enzymology Foreword by Nobel laureate Arieh Warshel, who first developed the EVB approach




Quantum-Mechanical Ab-initio Calculation of the Properties of Crystalline Materials


Book Description

A number of general-purpose, reasonably accurate and well-tested ab-initio codes for crystals are discussed in this book. The aim is to expand competence of their application in material sciences and solid-state physics. The book addresses particularly readers with a general knowledge in quantum chemistry and intends to give a deeper insight into the special algorithms and computational techniques in ab-initio computer codes for crystals. Three different programs which are available to all interested potential users on request are presented.







Monte Carlo Methods in Ab Initio Quantum Chemistry


Book Description

This book presents the basic theory and application of the Monte Carlo method to the electronic structure of atoms and molecules. It assumes no previous knowledge of the subject, only a knowledge of molecular quantum mechanics at the first-year graduate level. A working knowledge of traditional ab initio quantum chemistry is helpful, but not essential.Some distinguishing features of this book are: