Ab initio basis set and correlation limit interaction energies for He–He, He–H 2, and H–H 2

Abstract

An ab initio search for the exact nonrelativistic interaction energies for He–He, He–H 2, and H–H 2 systems was made by estimating the basis set limit CCSD(T) interaction energies from the extrapolation of counterpoise (CP) interaction energies with aug-cc-pV5Z and aug-cc-pV6Z basis sets by 1/( X−1) 3 ( X=5,6) and correcting for the difference between the FCI and CCSD(T) energies. While the result for He 2 is in perfect agreement with the exact quantum Monte Carlo result, the result for H 3 suggests the barrier height for colinear H+H 2→H 2+H reaction is close to 9.60 kcal/mol, ∼0.01 kcal/mol lower than the best result reported so far