Range-separated density-functional theory applied to the beryllium dimer and trimer

TL;DR

This study evaluates various range-separated density-functional theory variants for small beryllium clusters, finding that long-range coupled-cluster methods with a large range-separation parameter yield accurate potential energy curves.

Contribution

It systematically assesses the performance of range-separated density-functional methods on beryllium dimers and trimers, highlighting the importance of the range-separation parameter and coupled-cluster approaches.

Findings

Long-range second-order perturbation theory is insufficient.

Long-range coupled-cluster theory provides accurate potential energy curves.

A larger range-separation parameter (μ=1 bohr$^{-1}$) improves results.

Abstract

The beryllium dimer and trimer are, despite their small number of electrons, excellent systems for assessing electronic-structure computational methods. With reference data provided by multi-reference averaged coupled-pair functional calculations, we assess several variants of range-separated density-functional theory, combining long-range second-order perturbation theory or coupled-cluster theory with a short-range density functional. The results show that i) long-range second-order perturbation theory is not sufficient, ii) long-range coupled-cluster theory gives reasonably accurate potential energy curves, but iii) provided a relatively large value of $\mu=1$ bohr$^{-1}$ for the range-separationparameter is used. The article is dedicated to the memory of J\'anos G. \'Angy\'an.