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 lev el on di-nitrogen and neon interacting with a calcium (II) cation. The inte raction 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 combina tion rules are then applied in reverse to get A(Ca2+-Ca2+), b(Ca2+-Ca2+). C ombining these with values of A(NN), b(NN) enables the Ca2+-N-2 potential e nergy curves to be predicted a priori. Agreement with the ab initio data is found to improve dramatically when the anisotropy of the nitrogen polariza bility is included in the induced interaction energy. Other combination rul es are tried but are not found to have an impact on the agreement between t he a priori potential and the ab initio data.