Traditional Approach Analytic Potential Energy Surfaces

Traditional Approach Analytic Potential Energy Surfaces 

The traditional approach for performing classical trajectory simulations is to represent V(q) by either an empirical analytic function, with adjustable parameters, or as an analytic function fit in total or in part to ab initio potential energies. A widely used empirical potential is the London-Eyring-Polanyi-Sato function for triatomic systems. Since the number of independent coordinates is 3N — 6 for a nonlinear system with N atoms, to fit V(q) with potential energies for each internal coordinate at NP different positions, a total of (] p)3N-6 initio points are required. Thus, only for reactive systems with a small number of atoms is it practical to derive y(q) completely from 

Select initial q and p from an ensemble of trajectories with = //(p,q) + K(q) 

Determine final properties of each trajectory from the final q and p. 

An approach often used for large polyatomic systems is to derive, from ab initio calculations, an analytic potential energy function for the few degrees of freedom thought to be most critical for the dynamics, and use empirical 

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Traditional Approach Analytic Potential Energy Surfaces... 

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