A time-dependent formulation of multi-reference perturbation theory

TL;DR

This paper introduces a time-dependent approach to multi-reference perturbation theory, specifically a second-order method called t-NEVPT2, which improves computational efficiency and avoids complex matrix operations.

Contribution

It presents the development and implementation of a time-dependent formulation of second-order n-electron valence perturbation theory that reduces computational scaling and complexity.

Findings

t-NEVPT2 provides accurate energies for molecules like water, nitrogen, carbon, and chromium.

The method avoids high-order density matrices and metric diagonalization.

Results demonstrate improved efficiency over traditional methods.

Abstract

We discuss the time-dependent formulation of perturbation theory in the context of the interacting zeroth-order Hamiltonians that appear in multi-reference situations. As an example, we present a time-dependent formulation and implementation of second-order n-electron valence perturbation theory. The resulting t-NEVPT2 method yields the fully uncontracted n-electron valence perturbation wavefunction and energy, but has a lower computational scaling than the usual contracted variants, and also avoids the construction of high-order density matrices and the diagonalization of metrics. We present results of t-NEVPT2 for the water, nitrogen, carbon, and chromium molecules, and outline directions for the future.