Computational Chemistry: Reviews of Current Trends

The following sections are included:

• PREFACE

• CONTENTS

Recently developed Brillouin-Wigner coupled cluster theory in its single reference and multireference versions is discussed. Relation of this theory with standard coupled cluster approaches is discussed in details. Special attention is paid to various versions of multireference Brillouin-Wigner coupled cluster theory. New single-root (state specific) multireference Brillouin-Wigner coupled cluster theory is developed and the results of the calculations on selected molecules are presented. The method is relatively simple and the results are encouraging.

The theory and applications of the Model Core Potential method over the period of almost thirty years are reviewed. Several variants of the method are described and discussion of the applications of Version 1 is presented.

Bromine-containing species are more effective in depletion of stratospheric ozone, on a per-atom basis, than chlorine-containing species. The major known reservoirs of inorganic bromine are Br, HOBr, BrO and BrONO₂. However, in-situ studies of inorganic bromine partitioning in the stratosphere have suggested missing bromine reservoirs. This work explores the possible formation of other reservoirs of bromine that may result from reactions, which arise due to the coupling of bromine oxide species with atmospheric radicals from the HO_x, ClO_x and BrO_x chemical families. Computational studies examine the structural and energetic properties of the resulting products from atmospheric coupling reactions, and the possible new atmospheric chemistry.

A series of gas-phase radical sulfur compounds is examined. The bonding is characterized in terms of orbital descriptions, population analysis, vibrational frequencies and energetics. Several different bonding modes are found. As has been seen in the literature previously, 9-S-3 compounds (9 electrons around a 3-coordinate sulfur) may have the unpaired electron centered on just one atom or distributed over two or three centers. Both theoretical studies and the related experimental results are presented. Geometries are tabulated and compared to other compounds with the same elements.

A review of modern trends in quantum chemical modeling of solvent influence is presented. Current versions of the most popular schemes to model solvent influence have been described, and the correspondence between them has been established. Among the reviewed methods are ab initio molecular dynamics for the liquid state, ab initio and semiempirical continuum, and supermolecular approximations. Ab initio and semi-empirical methods are compared for a selected number of examples mainly dealing with solvent influence in hydrogen bondinga acid-base reactions and related phenomena.

The Internet is a tool whose potential applications to research and education are rapidly growing and evolving. The number of chemistry-related Web sites is expanding at a remarkable rate, new utilities are being devised, and the legions of researchers and educators making use of the new technologies are increasing daily. While a complete survey of relevant Internet resources is far beyond the scope of a single chapter, it is our goal in this article to provide an overview of the current state of Internet applications for chemists, and to highlight these generalizations with some specific examples. A discussion is provided on fundamental concepts of the Internet and the World-Wide Web. A selection of Internet tools and Web sites of possible interest to chemists are discussed, as is the phenomenon known as Internet publishing. The potential application of the Internet to university level instruction in chemistry is also explored. With the dramatic rate of expansion and evolution of both the resources available and the technology on which they are based, the authors can not claim to portray a definitive analysis of the entire scope of useful chemistry resources, nor is it feasible to treat the complete body of technology associated with current Internet development. Rather, this chapter details a number of utilities and sites which, within our frame of reference as computational scientists, have been of interest and use in our various endeavors. In order to provide readers with a more detailed and up-to-date reference, the authors have developed a Web based repository of related information (useful URLs, tutorials, etc.) in association with this article, and their research and educational activities.

The following sections are included:

• INDEX