Accelerating convergence to the thermodynamic limit with twist angle selection applied to methods beyond many-body perturbation theory

TL;DR

This paper introduces a method to select optimal twist angles using low-cost calculations, improving convergence to the thermodynamic limit in advanced quantum chemistry methods beyond coupled cluster, demonstrated with $i$-FCIQMC and MP2.

Contribution

The paper presents a novel twist angle selection scheme applicable to methods beyond coupled cluster, reducing computational effort for accurate thermodynamic limit extrapolation.

Findings

Selected twist angles yield energies matching twist-averaged results.

The method is effective for both $i$-FCIQMC and MP2.

Minimal code modifications are needed for implementation.

Abstract

We recently developed a scheme to use low-cost calculations to find a single twist angle where the couple cluster doubles energy of a single calculation matches the twist-averaged coupled cluster doubles energy in a finite unit cell. We used initiator full configuration interaction quantum Monte Carlo ($i$-FCIQMC) as an example of an exact method beyond coupled cluster doubles theory to show that this selected twist angle approach had comparable accuracy in methods beyond coupled cluster. Further, at least for small system sizes, we show that the same twist angle can also be found by comparing the energy directly (at the level of second-order Moller-Plesset theory) suggesting a route toward twist angle selection which requires minimal modification to existing codes which can perform twist averaging.