A well-scaling natural orbital theory

TL;DR

This paper presents a new energy functional based on natural spin-orbitals for efficient ground-state electronic structure calculations, achieving algebraic scaling and improved accuracy over existing density-functional methods.

Contribution

It introduces a novel energy functional using natural spin-orbitals and joint occupation probabilities, with scalable approximations and comparison to high-accuracy quantum chemistry results.

Findings

Algebraic scaling in energy calculations.

Results close to doubly occupied configuration interaction.

Better accuracy than current density-functional approximations.

Abstract

We introduce an energy functional for ground-state electronic structure calculations. Its variables are the natural spin-orbitals of singlet many-body wave functions and their joint occupation probabilities deriving from controlled approximations to the two-particle density matrix that yield algebraic scaling in general, and Hartree-Fock scaling in its seniority-zero version. Results from the latter version for small molecular systems are compared with those of highly accurate quantum-chemical computations. The energies lie above full configuration interaction calculations, close to doubly occupied configuration interaction calculations. Their accuracy is considerably greater than that obtained from current density-functional theory approximations and from current functionals of the one-particle density matrix.