Parameterization of a potential function for the Ca2+-Ne and Ca2+-N2 interactions using high-level ab initio data

Ab initio calculations have been carried out at the CCSD(T)/aug-cc-pVTZ level on di-nitrogen and neon interacting with a calcium (II) cation. The interaction of nitrogen with the Ca2+ cation is examined for end-on and side-on approaches. The two adjustable parameters in the TrAZ potential (A(Ca2+-Ne), b(Ca2+-Ne)) are fitted to the Ca2+-Ne potential energy curve and combination rules are then applied in reverse to get A(Ca2+-Ca2+), b(Ca2+-Ca2+). Combining these with values of A(NN), b(NN) enables the Ca2+-N-2 potential energy curves to be predicted a priori. Agreement with the ab initio data is found to improve dramatically when the anisotropy of the nitrogen polarizability is included in the induced interaction energy. Other combination rules are tried but are not found to have an impact on the agreement between the a priori potential and the ab initio data.