Downfolded Configuration Interaction for Chemically Accurate Electron Correlation

TL;DR

This paper introduces a novel downfolded configuration interaction method that efficiently achieves chemically accurate electron correlation by constructing a compact effective Hamiltonian through an iterative, deterministic process focused on local clusters.

Contribution

The method provides a new, efficient way to obtain accurate electron correlations without exhaustive configuration selection, improving computational chemistry techniques.

Findings

Achieves chemical accuracy in electron correlation calculations.

Demonstrates efficiency on multireference molecules.

Avoids full configuration space enumeration.

Abstract

A model subspace configuration interaction method is developed to obtain chemically accurate electron correlations by diagonalising a very compact effective Hamiltonian of realistic molecule. The construction of the effective Hamiltonian is deterministic and implemented by iteratively building a sufficiently small model subspace comprising local clusters of a small number of determinants. Through the low-rank reciprocal of interaction Hamiltonian, important determinants in the outer subspace are identified to couple with the subspace of pairwise clusters. This method avoids direct ordering and selection of the configurations in the entire space. We demonstrate the efficiency and accuracy of this theory for several molecules of the multireference nature relevant to chemistry.