Born-Oppenheimer potential for H$_2$

TL;DR

This paper presents a highly precise calculation of the Born-Oppenheimer potential for H₂ across a wide range of distances using analytic formulas, enabling high-accuracy diatomic molecule computations.

Contribution

It introduces an analytic method for calculating two-center two-electron integrals with exponential functions, achieving about 10^{-15} precision for H₂.

Findings

Achieved about 10^{-15} precision in potential calculations

Verified asymptotic exchange energy formulas

Provided analytic formulas for high-precision integrals

Abstract

The Born-Oppenheimer potential for the $^1\Sigma_g^+$ state of H$_2$ is obtained in the range of 0.1 -- 20 au, using analytic formulas and recursion relations for two-center two-electron integrals with exponential functions. For small distances James-Coolidge basis is used, while for large distances the Heitler-London functions with arbitrary polynomial in electron variables. In the whole range of internuclear distance about $10^{-15}$ precision is achieved, as an example at the equilibrium distance $r=1.4011$ au the Born-Oppenheimer potential amounts to $-1.174\,475\,931\,400\,216\,7(3)$. Results for the exchange energy verify the formula of Herring and Flicker [Phys. Rev. {\bf 134}, A362 (1964)] for the large internuclear distance asymptotics. The presented analytic approach to Slater integrals opens a window for the high precision calculations in an arbitrary diatomic molecule.