Molecular Electrostatic Potentials

Concepts and Applications

J.S. Murray, K. Sen

• Publisher: Elsevier Science
• Year: 1996
• ISBN:
  9780080536859
• Topic: Physical Sciences
• Subtopic: Electromagnetism

Over the past 25 years, the molecular electrostatic potential has become firmly established as an effective guide to molecular interactions. With the recent advances in computational technology, it is currently being applied to a variety of important chemical and biological systems. Its range of applicability has expanded from primarily a focus on sites for electrophilic and nucleophilic attack to now include solvent effects, studies of zeolite, molecular cluster and crystal behavior, and the correlation and prediction of a wide range of macroscopic properties. Moreover, the increasing prominence of density functional theory has raised the molecular electrostatic potential to a new stature on a more fundamental conceptual level. It is rigorously defined in terms of the electron density, and has very interesting topological characteristics since it explicitly reflects opposing contributions from the nuclei and the electrons.

This volume opens with a survey chapter by one of the original pioneers of the use of the electrostatic potential in studies of chemical reactivity, Jacopo Tomasi. Though the flow of the succeeding chapters is not stringently defined, the overall trend is that the emphasis changes gradually from methodology to applications. Chapters discussing more theoretical topics are placed near the end. Readers will find the wide variety of topics provided by an international group of authors both convincing and useful.

MEP: a tool for interpretation and prediction. From molecular structure to solvation effects

J. Tomasi^a and B. Mennucci^a, ^aDipartimento di Chimica e Chimica Industriale, University of Pisa, Via Risorgimento 35, 56100 Pisa, Italy

R. Cammi^b, ^bDipartimento di Chimica, University of Parma, Viale delle Scienze 1, 43100 Parma, Italy

1 Introduction

This paper aims at giving a partial view of the evolution of the research in the definition, and use, of semiclassical descriptions performed at Pisa over the years. We stress the emphasis on the adjective partial as, in writing this paper, we realized that it would have been too long to consider also the part of the research addressed to apply the semiclassical approach to the description of the internal structure of molecules.

We have thus limited our attention to molecular interactions. Even with this limitation, the exposition is quite long, as it seemed us convenient to insert what we have done, and we are still doing, in a broader framework, including also critical elaboration of methods and proposals suggested by other groups.

Our effort has thus assumed the aspect of an essay, where space has been given to methodological considerations, to the exposition of the motivations which led us, and other people, to do what has been done, and to the identification of the mutual interplay in the research programmes of various groups.

We hope to have been able to give a living picture of the evolution of scientific research on a specific theme. We also hope that this presentation will encourage young people to contribute further to this evolution. The three authors are of very different age, and the historical perspective given at some points, mainly reflects the experience of the elder (J.T.). However the paper has been collectively written, and reflects the working style (if it is possible to use this word) in our group, where both methodological considerations and critical appraisal of the evolution of the methodologies are subject to continuous discussions.

The paper is organized in four main sections:

1. Thirty years ago: the evolution of chemical quantum theory.

2. The molecular electrostatic potential as an interpretative tool for intermolecular interactions.

3. Intermolecular energy: a full decomposition at HF level.

4. Molecular electrostatics and semiclassical approximation in solvation effects.

In the first section we shall briefly consider the problems which Quantum Chemistry had to face at the beginning of the computational era (1959-1969) to put in the most appropriate contest the proposal of using the molecular electrostatic potential (MEP), which is the topic motivating this essay.

In the second section we shall analyze the properties and characteristics of the MEP as an interpretative tool for intermolecular interactions, in order to find a rationale of this function’s shape, and to analyze computationally convenient formulations to be used on larger molecular systems and for systematic applications. To this purpose we shall introduce a very important approach in the analysis of intermolecular interactions, namely to extract from the model the interactions which can be treated classically and to describe them at the most accurate level.

In the last two sections we shall describe some results of a systematic examination of the performances of this semiclassical model in dimers and in a specific class of many– molecules systems, i.e. the solutions, with the aim of putting in evidence the usefulness and the limits of this inherently approximate representation of chemical interactions.

2 Thirty Years Ago: The Evolution of Chemical Quantum Theory

In the early sixties the newly formed group of Theoretical Chemistry of the University of Pisa dedicated its main effort to elaborate methods and computer codes for ab initio quantum mechanical calculations, from the basic integrals (over Slater-type orbitals) to CI methods of various nature and complexity. The effort of several years of hard work, we think, was well rewarded: the set of combined computer programs computed there was one among the firsts, to be able to treat relatively complex molecules (say, with more than four atoms) within a large span of applications, from open and closed shell electronic structures at various levels of approximations, and with basis sets also including d functions, to a variety of properties, such as electric and magnetic response functions, electronic excitations, etc.

One of the fields considered for applications was the study of structure and properties of molecules of relatively large dimensions in their ground state. When the first extensive report, regarding several three-membered cyclic molecules [1], was submitted to the Journal of Chemical Physics, both the referees expressed, with different words, favourable comments about the problem of ‘what to do with wavefunctions computed with such a considerable effort’...

Table of contents

• Cover image
• Title page
• Table of Contents
• Theoretical and Computational Chemistry
• Front Matter
• Copyright page
• Foreword
• Acknowledgments
• MEP: a tool for interpretation and prediction. From molecular structure to solvation effects
• Molecular Electrostatic Potentials from Density Functional Theory
• The Use of Electrostatic Potential Fields in QSAR and QSPR
• Generalization of the Molecular Electrostatic Potential for the Study of Noncovalent interactions
• Molecular Recognition via Electrostatic Potential Topography
• Molecular electrostatic potentials and fields: hydrogen bonding, recognition, reactivity and modelling
• Molecular electrostatic potentials for large systems
• Protein electrostatics
• The Lorentz-Debye-Sack theory and dielectric screening of electrostatic effects in proteins and nucleic acids
• Modelling Intrinsic Basicities: The Use of the Electrostatic Potentials and the Atoms-in-Molecules Theory
• Computed electrostatic potentials in molecules, clusters, solids and biosystems containing transition metals
• Studies on the molecular electrostatic potential inside the microporous material and its relevance to their catalytic activity
• X-ray diffraction and the potential distribution in crystals
• Molecular Electrostatic Potentials vs. DFT descriptors of reactivity
• Electrostatic Potential, Bond Density and Bond Order in Molecules and Clusters
• Relationships of Electrostatic Potentials to Intrinsic Molecular Properties
• Index