Auxiliary-field quantum Monte Carlo calculations with multiple-projector pseudopotentials

TL;DR

This paper integrates multiple-projector pseudopotentials into the pw-AFQMC method, reducing computational costs and enabling accurate simulations of complex systems, with applications to materials like NaCl, Cu, and sulfur hydride.

Contribution

It introduces the implementation of multiple-projector pseudopotentials into pw-AFQMC, enhancing efficiency and transferability for large-scale and complex material simulations.

Findings

Demonstrated accuracy with NaCl and Cu calculations.

Validated DFT predictions against pw-AFQMC for sulfur hydride.

Reduced computational cost in large system simulations.

Abstract

We have implemented recently developed multiple-projector pseudopotentials into the planewave based auxiliary-field quantum Monte Carlo (pw-AFQMC) method. Multiple-projector pseudopotentials can yield smaller planewave cut-offs while maintaining or improving transferability. This reduces the computational cost of pw-AFQMC, increasing its reach to larger and more complicated systems. We discuss the use of non-local pseudopotentials in the separable Kleinman-Bylander form, and the implementation in pw-AFQMC of the multiple-projector optimized norm-conserving pseudopotential ONCVPSP of Hamann. The accuracy of the method is first demonstrated by equation-of-state calculations of the ionic insulator NaCl and more strongly correlated metal Cu. The method is then applied to calibrate the accuracy of density functional theory (DFT) predictions of the phase stability of recently discovered high temperature and pressure superconducting sulfur hydride systems. We find that DFT results are in good agreement with pw-AFQMC, due to near cancellation of electron-electron correlation effects between different structures.