Ab initio atom-atom potentials using CamCASP: Many-body potentials for the pyridine dimer

TL;DR

This paper develops accurate, first-principles many-body atom-atom potentials for pyridine, demonstrating improved modeling of dimers with new stable minima and systematic enhancements over empirical potentials.

Contribution

It introduces a systematic methodology using CamCASP for creating highly accurate, first-principles many-body potentials for pyridine, including discovery of new stable minima.

Findings

Achieved r.m.s. errors of about 0.6kJ mol-1 for pyridine dimers

Supported eight stable minima, four previously unreported

Systematic improvements possible without significant human effort

Abstract

In Part I of this two-part investigation we described a methodology for the development of robust, analytic, many-body atom-atom potentials for small organic molecules from first principles and demonstrated how the CamCASP program can be used to derive the damped, distributed multipole models for pyridine. Here we demonstrate how the theoretical ideas for the short-range models described in Part I, which are implemented in the CamCASP suite of programs, can be used to develop a series of many-body potentials for the pyridine system. Even the simplest of these potentials exhibit r.m.s. errors of only about 0.6kJ mol-1 for the low-energy pyridine dimers, significantly surpassing the best empirical potentials. Our best model is shown to support eight stable minima, four of which have not been reported in the literature before. Further, the functional form can be made systematically more elaborate so as to improve the accuracy without a significant increase in the human-time spent in their generation. We investigate the effects of anisotropy, rank of multipoles, and choice of polarizability and dispersion models.