Accurate molecular dynamics and nuclear quantum effects at low cost by multiple steps in real and imaginary time: using density functional theory to accelerate wavefunction methods

TL;DR

This paper introduces a computationally efficient method combining multiple time step integrators and ring-polymer contraction to accurately simulate nuclear quantum effects at high electronic structure levels, demonstrated on the Zundel cation.

Contribution

It presents a novel approach that significantly reduces the computational cost of quantum nuclear simulations using density functional theory and wavefunction methods.

Findings

Reduces overhead of nuclear quantum effect modeling to near zero.

Successfully applied to MP2 and semi-local DFT for the Zundel cation.

Compatible with other cost-reduction techniques for path integral calculations.

Abstract

The development and implementation of increasingly accurate methods for electronic structure calculations mean that, for many atomistic simulation problems, treating light nuclei as classical particles is now one of the most serious approximations. Even though recent developments have significantly reduced the overhead for modelling the quantum nature of the nuclei, the cost is still prohibitive when combined with advanced electronic structure methods. Here we present how multiple time step integrators can be combined with ring-polymer contraction techniques (effectively, multiple time stepping in imaginary time) to reduce virtually to zero the overhead of modelling nuclear quantum effects, while describing inter-atomic forces at high levels of electronic structure theory. This is demonstrated for a combination of MP2 and semi-local DFT applied to the Zundel cation. The approach can be seamlessly combined with other methods to reduce the computational cost of path integral calculations, such as high-order factorizations of the Boltzmann operator, or generalized Langevin equation thermostats.