A new class of reaction path based potential energy surfaces enabling accurate black box chemical rate constant calculations.

Abstract

A new method for constructing a full-dimensional potential energy surface representation in black-box fashion for an arbitrary reaction is presented. With limited knowledge of the system and with a limited number of reference-level data points, it is possible to calculate reaction rate constants with high quality. Building on our recently published application of Grimme's quantum-mechanically derived force field (QMDFF) and its empirical valence bond extension EVB-QMDFF to rate constant calculations, an improved EVB coupling method with local corrections was developed in order to avoid spurious problems for certain systems and hence to achieve an even wider range of applicability. A given reaction path (RP) is modeled as a parametric curve via cubic spline interpolation; regions offside this path are then extrapolated with quadratic Taylor series, and regions around the transition state are corrected by introduction of direct reference interpolation; the method is named transition region corrected RP-EVB-QMDFF (TREQ). To verify the quality of TREQ, six reactions were chosen for which full-dimensional analytical potential surfaces are available in the literature. Chemical reaction rates were calculated with ring polymer molecular dynamics on the reference surfaces as well as on the TREQ surfaces resulting in excellent agreement.