Ab initio potential energy curve for the ground state of beryllium dimer

TL;DR

This paper presents highly accurate ab initio calculations of the beryllium dimer's potential energy curve, including relativistic and quantum electrodynamics effects, achieving results that closely match experimental data.

Contribution

The study provides the first comprehensive ab initio potential energy curve for Be₂, incorporating relativistic and quantum electrodynamics effects with high-level electronic structure methods.

Findings

Predicted well-depth D_e=934.5±2.5 cm⁻¹ closely matches experimental data.

Confirmed the existence of the weakly bound twelfth vibrational level.

Quantum electrodynamics effects significantly influence the potential energy calculations.

Abstract

This work concerns \emph{ab initio} calculations of the complete potential energy curve and spectroscopic constants for the ground state $X^1\Sigma_g^+$ of the beryllium dimer, Be$_2$. High accuracy and reliability of the results is one of the primary goals of the paper. To this end we apply large basis sets of Slater-type orbitals combined with high-level electronic structure methods including triple and quadruple excitations. The effects of the relativity are also fully accounted for in the theoretical description. For the first time the leading-order quantum electrodynamics effects are fully incorporated for a many-electron molecule. Influence of the finite nuclear mass corrections (post-Born-Oppenheimer effects) turns out to be completely negligible for this system. The predicted well-depth ($D_e=934.5\pm2.5\,\mbox{cm}^{-1}$) and the dissociation energy ($D_0=808.0\,\mbox{cm}^{-1}$) are in a very good agreement with the most recent experimental data. We confirm the existence of the weakly bound twelfth vibrational level [Patkowski et al., Science 326, 1382 (2009)] and predict that it lies just about 0.5 $\mbox{cm}^{-1}$ below the onset of the continuum.