Correlation Energy Divergences in Metallic Systems

TL;DR

This paper investigates the divergence issues in total energy calculations of metallic systems using various many-body theories, highlighting the suitability of non-perturbative methods like coupled cluster over perturbative approaches.

Contribution

It provides a comparative analysis of divergence behaviors in different many-body methods for metals, emphasizing the viability of non-perturbative coupled cluster theories.

Findings

Non-perturbative coupled cluster methods are suitable for metals.

Perturbative coupled cluster methods exhibit divergences.

RPA energies serve as a benchmark for testing divergences.

Abstract

We numerically examine divergences of the total energy in metallic systems of approximate many-body theories using Hartree--Fock as a reference, including perturbative (M\oller-Plesset, MP), coupled cluster (CC) and configuration interaction (CI) approaches. Controlling for finite size effects and basis set incompleteness error by comparison with energies from the random phase approximation (RPA), we suggest convincingly that non-perturbative coupled cluster theories are acceptable for modelling electronic interactions in metals whilst perturbative coupled cluster theories are not. Data are provided from the RPA with which it is possible to test other approximate finite-basis methods for divergences with only modest computational cost.