Correct quantum chemistry in a minimal basis from effective Hamiltonians

TL;DR

This paper introduces a method to generate effective Hamiltonians that accurately model chemical properties and excited states using minimal basis sets, leveraging canonical transformations to fold correlation from larger bases.

Contribution

It presents a novel approach to create ab-initio effective Hamiltonians that maintain qualitative accuracy in chemistry with minimal basis sets, using canonical transformations.

Findings

Accurately captures excited states in water, nitrogen, and ethylene.

Successfully describes bond-breaking in nitrogen and chromium dimer.

Effective Hamiltonians perform well with minimal basis sets.

Abstract

We describe how to create ab-initio effective Hamiltonians that qualitatively describe correct chemistry even when used with a minimal basis. The Hamiltonians are obtained by folding correlation down from a large parent basis into a small, or minimal, target basis, using the machinery of canonical transformations. We demonstrate the quality of these effective Hamiltonians to correctly capture a wide range of excited states in water, nitrogen, and ethylene, and to describe ground and excited state bond-breaking in nitrogen and the chromium dimer, all in small or minimal basis sets.