Interpolated wave functions for nonadiabatic simulations with the fixed-node quantum Monte Carlo method

TL;DR

This paper introduces a new interpolated wave function ansatz for nonadiabatic simulations using fixed-node quantum Monte Carlo, improving energy estimates for the CH molecule by better capturing nonadiabatic effects.

Contribution

The authors propose a novel wave function form that interpolates determinant coefficients from configuration interaction calculations, enhancing nonadiabatic energy simulations.

Findings

Reduced nonadiabatic energy contribution in CH molecule

Improved wave function accuracy over previous models

CH molecule shows the largest nonadiabatic effects among studied molecules

Abstract

Simulating nonadiabatic effects with many-body wave function approaches is an open field with many challenges. Recent interest has been driven by new algorithmic developments and improved theoretical understanding of properties unique to electron-ion wave functions. Fixed-node diffusion Monte Caro is one technique that has shown promising results for simulating electron-ion systems. In particular, we focus on the CH molecule for which previous results suggested a relatively significant contribution to the energy from nonadiabatic effects. We propose a new wave function ansatz for diatomic systems which involves interpolating the determinant coefficients calculated from configuration interaction methods. We find this to be an improvement beyond previous wave function forms that have been considered. The calculated nonadiabatic contribution to the energy in the CH molecule is reduced compared to our previous results, but still remains the largest among the molecules under consideration.