Nonunitary projective transcorrelation theory inspired by the F12 ansatz

TL;DR

This paper introduces a novel nonunitary projective transcorrelation method inspired by F12 theory, which simplifies the effective Hamiltonian and improves accuracy by satisfying cusp conditions without spin contamination.

Contribution

It presents a new nonunitary transcorrelation approach that terminates at four-body interactions and satisfies cusp conditions, enhancing computational efficiency and accuracy.

Findings

Effective Hamiltonian terminates at four-body interactions.

No spin contamination within the non-relativistic framework.

Improved accuracy in small molecule applications.

Abstract

An alternative nonunitary transcorrelation, inspired by the F12 ansatz, is investigated. In contrast to the Jastrow transcorrelation of Boys-Handy, the effective Hamiltonian of this projective transcorrelation features: 1. a series terminating formally at four-body interactions. 2. no spin-contamination within the non-relativistic framework. 3. simultaneous satisfaction of the singlet and triplet first-order cusp conditions. 4. arbitrary choices of pairs for correlation including frozen core approximations. We discuss the connection between the projective transcorrelation and F12 theory with applications to small molecules, to show that the cusp conditions play an important role to reduce the uncertainty arising from the nonunitary transformation.