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 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 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.