Preface
The explaration, characterization, and representation of potential energy hypersurfaces (PES) of chemical syeteme consisting of N interacting atoms is a task af increasing importance especially as a hasis for modern reactivity theory.
In Chap. 1 of this hook, meaning and problems of the potential surface concept are summarized. The mathematical analysis of the PES is subject of the Chapters 2 and 3. It covers the calculation and characterization of chemically interesting points, curves and global situations on a reaction PES. Since adequate mathematicaI representations are of increasing importance for the informative processes within the chemical community, the presentation of the mathematical methods in this book also implies educational aspects. Finally, the dependence of PES properties on those approximations is considered which occur in the usual application of quantum chemical theory. This presentation may give the chance to deepen the chemist's PES intuition concerning the handling af reaction PES as a source for microscopic and macroscopic information with and without medium influence (Chap. 4). Thus, we hope to stimulate theoreticaI understanding and research. Considering the importance of proton transfer reactions in chemistry and biology as well as their advantages in a theoretical treatment, they form the main source for selected examplea in Chap. 4. For a full account of experimental and theoretical work in this field, we refer to excellent reviews in the literature.
As soon as PuIay's pioneering work on the problem of quantum chemical geometry optimization was supported by important contributions of McIver and Komornicki in the early seventies, the utilization of the gradient of potential energy has revolutionized the a priori calculation of chemical reactivity. The gradient concept was suitable as a basis for a systematic study of chemical reactions and the further development of reaction theory. In 1973, one of the authors (D.H.) published his first quantum chemical program system with some applications using the gradient of the potential energy in semiempirical methods. The main interest was in the structure and stability of carbocations forming intermediates in important chemical standard reactions.
Later on, we started a cooperation between the Departments of Chemistry and Mathematics at our University to improve the possibilities of PES analysis. At present our work follows three main directions:
- development of mathematical methods far the analysis of PES,
- application of quantum chemical ab initio methods on models of chemical standard reactions (exploration of reaction mechanism),
- the role of vibrations and intramolecular vibrational redistribution (IVR) during a reaction.
We hope that our experience and results gained in these fields will enrich this book. Dietmar Heidrich is responsible for Chaps. l and 4, Wolfgang Kliesch is the leading author for Chap. 2 (up to 2.5), Wolfgang Quapp from 2.6 up to Chap.3.
We would like to thank some colleagues for their help and support to overcome problems and to finish this book:
Dr.S.Ackermann (Leipzig, Germany),
Dr.J.Pancir (Prague, Czechoslovakia),
Dr.J.Reinhold (Leipzig, Germany),
Prof.Dr.P.v.R.Schleyer (Erlangen, Germany),
Prof.Dr.Z.Slanina (Prague, Czechoslovakia),
Prof.Dr.C.Weiss (Leipzig, Germany),
Prof.Dr.M. and Dr.B.Winnewiaser (Gießen, Germany),
Prof.Dr.R.Zahradnik (Prague, Czechoslovakia).
Special thanks should be given to
Doz.Dr.H.-J.Hofmann (Leipzig, Germany),
Prof.Dr.J.Tomasi (Pisa, Italy)
who have substantially contributed to this work.
Wolfgang Quapp would like to express his appreciation to the Fonds der chemischen Industrie and the Deutsche Forschungsgemeinschatt for supporting in part this work.
Leipzig, April 1991, D.H., W.K and W.Q.
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