Systematic improvement of trial states in phaseless auxiliary-field quantum Monte Carlo

Journal Article · Wed Jan 01 00:00:00 EST 2025 · arXiv

DOI:https://doi.org/10.48550/arXiv.2510.06486· OSTI ID:3025743

Kjønstad, Eirik F.; Damour, Yann; Sharma, Sandeep; Chan, Garnet Kin-Lic

We extend the use of coupled cluster (CC) trial states in the phaseless auxiliary-field quantum Monte Carlo (AFQMC) method beyond single and double excitations to include both triple and quadruple excitations. With this AFQMC/CC hierarchy, we are able to systematically benchmark the method's performance on molecular systems as the quality of the trial is improved. Our results show that the phaseless AFQMC energy improves systematically and is typically significantly more accurate than the energy of the underlying trial state. However, the relative improvement compared to the trial CC energy decreases as we ascend the CC hierarchy. As the CC wavefunction is usually further approximated when used as an AFQMC trial, we also explore the relationship between the components of the CC wavefunction and the resulting AFQMC/CC error. Our results suggest that improving the representation of the CC wave function in the AFQMC trial does not always lower the bias even when it increases the fidelity of the trial with the exact ground state.

• Research Organization: arXiv
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE)
• Grant/Contract Number: SC0018140
• OSTI ID: 3025743
• Journal Information: arXiv, Journal Name: arXiv
• Country of Publication: United States
• Language: English

Related Subjects

Chemical Physics (physics.chem-ph)
FOS: Physical sciences