RPA natural orbitals and their application to post-Hartree-Fock electronic structure methods

TL;DR

This paper introduces a method using RPA-derived natural orbitals to efficiently approximate post-Hartree-Fock correlation energies, demonstrating rapid convergence and high accuracy for small systems and periodic materials.

Contribution

The paper presents a novel approach to approximate correlation energies using RPA natural orbitals, improving efficiency and accuracy over traditional methods.

Findings

RPA natural orbitals rapidly converge MP2 correlation energy

Full CI energies for He and H2 agree with literature and experiments

Method offers a computationally efficient way to approximate correlation energies

Abstract

We present a method to approximate post-Hartree-Fock correlation energies by using approximate natural orbitals obtained by the random phase approximation (RPA). We demonstrate the method by applying it to the helium atom, the hydrogen and fluorine molecule, and to diamond as an example of a periodic system. For these benchmark systems, we show that RPA natural orbitals converge the MP2 correlation energy rapidly. Additionally, we calculated full configuration interaction energies for He and H$_2$, which are in excellent agreement with the literature and experimental values. We conclude that the proposed method may serve as a compromise to reach good approximations to correlation energies at moderate computational cost, and we expect the method to be especially useful for theoretical studies on surface chemistry by providing an efficient basis to correlated wave function based methods.