Noncovalent Interactions by QMC: Speedup by One-Particle Basis-Set Size Reduction

TL;DR

This paper demonstrates that truncating the one-particle basis sets in FN-DMC calculations can significantly reduce computational cost without compromising accuracy in noncovalent interaction energy estimates.

Contribution

It introduces a basis-set truncation scheme for FN-DMC guiding functions that maintains accuracy while reducing computational resources.

Findings

Basis-set truncation has negligible impact on energy difference accuracy.

The scheme reduces local energy variance and computational cost.

Triple zeta basis sets suffice for benchmark accuracy in small complexes.

Abstract

While it is empirically accepted that the fixed-node diffusion Monte-Carlo (FN-DMC) depends only weakly on the size of the one-particle basis sets used to expand its guiding functions, limits of this observation are not settled yet. Our recent work indicates that under the FN error cancellation conditions, augmented triple zeta basis sets are sufficient to achieve a benchmark level of 0.1 kcal/mol in a number of small noncovalent complexes. Here we report on a possibility of truncation of the one-particle basis sets used in FN-DMC guiding functions that has no visible effect on the accuracy of the production FN-DMC energy differences. The proposed scheme leads to no significant increase in the local energy variance, indicating that the total CPU cost of large-scale benchmark noncovalent interaction energy FN-DMC calculations may be reduced.