Electron affinity of LiH^-

Abstract

In this work we present high-accuracy benchmark-quality calculations of the electron affinity (EA) of the LiH molecule in a framework that does not assume the Born–Oppenheimer (BO) approximation. The EA is calculated as a difference between the total energies of ${\text{LiH}}^{-}$ and LiH. The calculations of the energies are performed using the Rayleigh-Ritz variational method with large basis sets of all-particle explicitly correlated Gaussian functions (ECGs). Up to 14,000 ECGs are used in the calculations for each system. The nonlinear parameters of the ECGs are optimised by by the minimisation of the total non-relativistic energy of the system using an approach that employs the energy gradient determined with respect the parameters. The ${\text{LiH}}^{-}$ and LiH non-relativistic non-BO wave functions are subsequently used to calculate the leading relativistic corrections. The calculated EA is well converged in terms of the size of the basis sets and the obtained value falls within the uncertainty of the best available experimental result.

GRAPHICAL ABSTRACT

Keywords:

• Electron affinity
• explicitly correlated basis sets
• non-Born–Oppenheimer

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work has been supported by Nazarbayev University [faculty development grant No. 021220FD3651], and the National Science Foundation [grant number 1856702]. L.A. acknowledges the support of the Centre for Advanced Study (CAS), the Norwegian Academy of Science and Letters, in Oslo, Norway, which funds and hosts our research project titled: Attosecond Quantum Dynamics Beyond the Born–Oppenheimer Approximation, during the 2021–2022 academic year. The authors are grateful to the University of Arizona Research Computing for providing computational resources for this work. Part of the calculations were performed on Shabyt HPC cluster at Nazarbayev University.