ipie: A Python-Based Auxiliary-Field Quantum Monte Carlo Program with Flexibility and Efficiency on CPUs and GPUs

• Published in: Journal of chemical theory and computation 2023-01, Vol.19 (1), p.109-121
• Main Authors: Malone, Fionn D., Mahajan, Ankit, Spencer, James S., Lee, Joonho
• Format: Article
• Language: English
• Subjects: Benchmarks; Central processing units; Configuration interaction; CPUs; Electrons; Graphics processing units; Isomerization; Monte Carlo Method; Quantum Electronic Structure; Wave functions
• ISSN: 1549-9618; 1549-9626
• DOI: 10.1021/acs.jctc.2c00934

We report the development of a python-based auxiliary-field quantum Monte Carlo (AFQMC) program, ipie, with preliminary timing benchmarks and new AFQMC results on the isomerization of [Cu2O2]2+. We demonstrate how implementations for both central and graphical processing units (CPUs and GPUs) are achieved in ipie. We show an interface of ipie with PySCF as well as a straightforward template for adding new estimators to ipie. Our timing benchmarks against other C++ codes, QMCPACK and Dice, suggest that ipie is faster or similarly performing for all chemical systems considered on both CPUs and GPUs. Our results on [Cu2O2]2+ using selected configuration interaction trials show that it is possible to converge the ph-AFQMC isomerization energy between bis­(μ-oxo) and μ-η2:η2 peroxo configurations to the exact known results for small basis sets with 105–106 determinants. We also report the isomerization energy with a quadruple-zeta basis set with an estimated error less than a kcal/mol, which involved 52 electrons and 290 orbitals with 106 determinants in the trial wave function. These results highlight the utility of ph-AFQMC and ipie for systems with modest strong correlation and large-scale dynamic correlation.