Fast Semistochastic Heat-Bath Configuration Interaction

TL;DR

This paper introduces an optimized semistochastic heat-bath configuration interaction method that significantly increases the size of the variational wavefunction and improves accuracy in complex many-electron calculations.

Contribution

The paper details a fast, parallelized SHCI algorithm that handles two orders of magnitude more determinants than previous methods, enabling highly accurate quantum chemistry calculations.

Findings

Achieved a benchmark energy for the chromium dimer with 2 billion determinants.

Included perturbative contributions from trillions of determinants with microhartree accuracy.

Demonstrated scalability and efficiency improvements in the SHCI algorithm.

Abstract

This paper presents in detail our fast semistochastic heat-bath configuration interaction (SHCI) method for solving the many-body Schrodinger equation. We identify and eliminate computational bottlenecks in both the variational and perturbative steps of the SHCI algorithm. We also describe the parallelization and the key data structures in our implementation, such as the distributed hash table. The improved SHCI algorithm enables us to include in our variational wavefunction two orders of magnitude more determinants than has been reported previously with other selected configuration interaction methods. We use our algorithm to calculate an accurate benchmark energy for the chromium dimer with the X2C relativistic Hamiltonian in the cc-pVDZ-DK basis, correlating 28 electrons in 76 spatial orbitals. Our largest calculation uses two billion Slater determinants in the variational space, and semistochastically includes perturbative contributions from at least trillions of additional determinants with better than 10 microhartree statistical uncertainty.