Configuration Interaction with Antisymmetrized Geminal Powers

TL;DR

This paper introduces an extension of the STD-CI method using antisymmetrized geminal powers, achieving rapid convergence and efficient computation for quantum systems by leveraging different molecular orbitals.

Contribution

It develops an AGP-based scheme that enhances the STD-CI method with variational degrees of freedom, improving accuracy and convergence speed.

Findings

Rapid energy convergence within 0.72 μHartree for water molecule

Fast convergence observed in Hubbard tetramers

Computational cost scales as the fifth power of electrons and square of series terms

Abstract

To avoid the combinatorial computational cost of configuration interaction (CI), we have previously introduced the symmetric tensor decomposition CI (STD-CI) method, where we take advantage of the antisymmetric nature of the electronic wave function and express the CI coefficients compactly as a series of Kronecker product states (STD series) [W. Uemura and O. Sugino, Phys. Rev. Lett. 109, 253001 (2012)]. Here we extend the variational degrees of freedom by using different molecular orbitals for different terms in the STD series. This scheme is equivalent to the linear combination of the Hartree-Fock-Bogoliubov state or the antisymmetrized geminal powers (AGP). The total energy converges very rapidly within 0.72 $\mu$Hartree taking only 10 terms for the water molecule, and the convergence is likewise fast for Hubbard tetramers. The computational cost scales as the fifth power of the number of electrons and the square of the number of terms in the STD series, indicating the promise of this AGP-based scheme for highly accurate and efficient computation of quantum systems.