The performance of phaseless auxiliary-field quantum Monte Carlo on the ground state electronic energy of benzene

TL;DR

This paper evaluates the accuracy of phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) in calculating the ground state energy of benzene, demonstrating its effectiveness with simple trial wavefunctions and providing benchmark results.

Contribution

The study applies ph-AFQMC to benzene's ground state, comparing different trial wavefunctions and providing benchmark energies across basis sets, showcasing its accuracy and scalability.

Findings

ph-AFQMC+RHF deviates by -3.1(3) mE_h from consensus value

ph-AFQMC+CAS(6,6) deviates by -1.3(4) mE_h from consensus

Benchmark frozen core correlation energies provided for cc-pVTZ and cc-pVQZ

Abstract

The ground state electronic energy of benzene is the focus of a recent blind test by Eriksen and co-workers [arXiv:2008.02678]. In this note, we report the phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) results on the identical problem. We examine trial wavefunctions of the spin-restricted Hartree-Fock (RHF), and complete active space self-consistent field (CASSCF) with an active space of 6-electron and 6-orbital (i.e., CAS(6,6)) form for the cc-pVDZ basis set. ph-AFQMC+RHF deviates from the value where many methods agreed on (i.e., -863 m$E_h$) by -3.1(3) m$E_h$ whereas ph-AFQMC+CAS(6,6) deviates from the same value by -1.3(4) m$E_h$. In addition to this, we report the frozen core correlation energy of ph-AFQMC+RHF in the cc-pVTZ and cc-pVQZ basis sets as well as their complete basis set limit. Our findings highlight the accuracy, flexibility, and scalability of ph-AFQMC with simple trial wavefunctions.