Calculation of two-centre two-electron integrals over Slater-type orbitals revisited. III. Case study of the beryllium dimer

TL;DR

This paper presents highly accurate ab-initio calculations of the beryllium dimer's interaction energy using advanced Slater-type orbital basis sets, including relativistic and QED effects, achieving results in excellent agreement with experiments.

Contribution

It introduces new STO basis sets for beryllium, incorporates relativistic and QED corrections, and provides the most precise ab-initio interaction energy for the beryllium dimer to date.

Findings

Interaction energy of 929.0 ± 1.9 cm^{-1}

Relativistic effects are significant

QED effects are estimated

Abstract

In this paper we present results of ab-initio calculations for the beryllium dimer with basis set of Slater-type orbitals (STOs). Nonrelativistic interaction energy of the system is determined using the frozen-core full configuration interaction calculations combined with high-level coupled cluster correction for inner-shell effects. Newly developed STOs basis sets, ranging in quality from double to sextuple zeta, are used in these computations. Principles of their construction are discussed and several atomic benchmarks are presented. Relativistic effects of order ${\alpha}^2$ are calculated perturbatively by using the Breit-Pauli Hamiltonian and are found to be significant. We also estimate the leading-order QED effects. Influence of the adiabatic correction is found to be negligible. Finally, the interaction energy of the beryllium dimer is determined to be 929.0$\,\pm\,$1.9 $cm^{-1}$, in a very good agreement with the recent experimental value. The results presented here appear to be the most accurate ab-initio calculations for the beryllium dimer available in the literature up to date and probably also one of the most accurate calculations for molecular systems containing more than four electrons.