Computational Chemistry and Molecular Modeling
Atomic, Molecular and Optical Physics
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
A heuristic fitting procedure to obtain an analytical potential function for describing a reactive potential energy surface in the neighborhood of the intrinsic reaction coordinate (IRC) has been developed. For discussion, the pairwise potential function form, ∑anr-n, is assumed in order to fit ab initio quantum mechanical calculations of intramolecular (or intrasupermolecular) interaction energies and its use is found advantageous because all the calculation can be carried out by the linear least squares method. Normal modes perpendicular to IRC are utilized to prepare an initial data base for the potential fitting in the neighborhood of IRC. Some trial molecular dynamics (MD) simulations are performed in order to check the fitted potential function and, unless they lead to reasonable energies within the tolerance assumed, their results are utilized to construct an improved data base (the dynamic sampling). The present systematic optimization procedure has been applied to the proton transfer reaction of the formamidine-water (FW) system. The normal mode analysis in both the transition state (TS) and the stable state (SS) regions suggests that the present fitted potential function can reproduce satisfactorily the Born-Oppenheimer (BO) adiabatic surface obtained by ab initio molecular orbital (MO) calculations. We conclude that our procedure works well for the chemical reaction molecular dynamics (CRMD) simulation.
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