[...]... into Coulombic, polarization, exchange, dispersion, and charge–transfer terms; however, its direct adaptation to W(M/S), assimilating M to A and S to B presents some inconveniences Some analogous considerations apply to other partitions of In the EH–CSD approach it is not convenient to decouple electrostatic terms into rigid Coulombic and polarization contributions: the effective Hamiltonian leads to. .. chemical concepts In order to perform this analysis we need to define and use appropriate theoretical and computational tools The literature offers quite a large number of tools satisfying these basic requirements, but to consider all of them adequately would require a separate review We shall limit ourselves to a few remarks, mainly regarding application to reactions in solution Many tools regard subunits... frequencies To use the Hamiltonian associated to this definition of the poten- tial energy one has to consider coupling terms among the motions along s and the coordinates These couplings are called curvature coupling coefficients because they measure to what extent the trajectory may curve in a particular transverse coordinate The method is quite computer–demanding: one has to compute and to diagonalize... processes We hope that this book will contribute to this progress The Editors QUANTUM MECHANICAL MODELS FOR REACTIONS IN SOLUTION J TOMASI, B MENNUCCI Dipartimento di Chimica e Chimica Industriale, Università di Pisa Via Risorgimento 35, Pisa, Italy R CAMMI Dipartimento di Chimica, Università di Parma Viale delle Scienze 1, Parma, Italy AND M COSSI Dipartimento di Chimica, Università “Federico II” di Napoli... contributions related to the interaction potential However, their presence requires the consideration of further aspects of the computational problem, that may result to be critical in assessing the soundness of the study This is the reason why we put this Section before those devoted to methods, in order to highlight the specific computational points deserving more attention when applications to chemical reactions... related to an effective Hamiltonian containing a solute–solvent interaction term, In the implementation of the EH–CSD model, that will be examined in Section 6, use is made of the equilibrium solute–solvent potential There are good reasons to do so; however, when the attention is shifted to a dynamical problem, we have to be careful in the definition of This operator may be formally related to a response... conceptually simple, requires a serious consideration of the computational tools one has to select 4.2 REACTION MECHANISMS Nowadays the study of a reaction mechanism may be done by performing a well determined sequence of computational steps: we define this sequence as the canonical approach to the study of chemical reactions At first, one has to define the geometry of reagents and products, then that... 1981; Miertuš and Tomasi, 1982) We shall consider other versions later, and the differences with respect to PCM will be highlighted Other approaches, based on effective Hamiltonians expressed in terms of discrete solvent distributions, EH–DSD, or not relying on effective Hamiltonians, will also be considered Limitations of space make impossible a thorough consideration of all the topics here mentioned;... dispersion–repulsion ele- ments, etc.) These local components may be further partitioned according to the source from which they derive (for example, apparent charges due to different chemical groups), and used to elaborate tools In fact, if we con- dense the information they carry to a limited number of scalar quantities, the resulting tools may assess the influence of specific solvent/molecular group interactions in... into two broad classes, i.e reaction equilibria and reaction mechanisms Mechanisms, in turn, may be considered either at a static level or including dynamical aspects It is convenient to treat these items separately 4.1 REACTION EQUILIBRIA To study reaction equilibria we simply need to know the values of G(R) corresponding to two local minima (reagents and products) If we confine our consideration to . h1" alt="" COMPUTATIONAL APPROACHES TO BIOCHEMICAL REACTIVITY Understanding Chemical Reactivity Volume 19 Series Editor Paul G. Mezey, University of Saskatchewan, Saskatoon, Canada Editorial Advisory. finding a proton near a proton acceptor does not mean that the barrier for proton transfer is reduced by the given active site. Finally we would like to warn about the use of combined QM/MM approaches. . (eds.), Computational Approaches to Biochemical Reactivity, 1–102. © 1997 Kluwer Academic Publishers. Printed in the Netherlands. 2 ternal degrees of freedom. A limited number of collisions leads to