Non-Orthogonal Multi-Slater Determinant Expansions in Auxiliary Field Quantum Monte Carlo

TL;DR

This study demonstrates that non-orthogonal multi-Slater determinant expansions can produce compact, high-quality trial wave-functions for AFQMC, significantly improving accuracy in molecular energetics with relatively few determinants.

Contribution

It introduces and validates the use of non-orthogonal multi-Slater determinants in AFQMC to achieve high accuracy with compact trial wave-functions, outperforming traditional methods.

Findings

High accuracy with 10-20 determinants for G1 molecules

Significant error reduction in total and absorption energies

Favorable comparison with DMRG and CCSD(T) for isomerization path

Abstract

The Auxiliary-Field Quantum Monte Carlo (AFQMC) algorithm is a powerful quantum many-body method that can be used successfully as an alternative to standard quantum chemistry approaches to compute the ground state of many body systems, such as molecules and solids, with high accuracy. In this article we use AFQMC with trial wave-functions built from non-orthogonal multi Slater determinant expansions to study the energetics of molecular systems, including the 55 molecules of the G1 test set and the isomerization path of the $[Cu_{2}O_{2}]^{2+}$ molecule. The main goal of this study is to show the ability of non-orthogonal multi Slater determinant expansions to produce high-quality, compact trial wave-functions for quantum Monte Carlo methods. We obtain systematically improvable results as the number of determinants is increased, with high accuracy typically obtained with tens of determinants. Great reduction in the average error and traditional statistical indicators are observed in the total and absorption energies of the molecules in the G1 test set with as few as 10-20 determinants. In the case of the relative energies along the isomerization path of the $[Cu_{2}O_{2}]^{2+}$, our results compare favorably with other advanced quantum many-body methods, including DMRG and complete-renormalized CCSD(T). Discrepancies in previous studies for this molecular problem are identified and attributed to the differences in the number of electrons and active spaces considered in such calculations.