Theoretical investigation of Ca center dot RG, Ca+center dot RG, and Ca2+center dot RG (RG=Ar and Ne) complexes

The ground state structure, harmonic frequency, and dissociation energy for Ca . RG, Ca+. RG, and Ca2+. RG (RG=Ar and Ne) complexes are computed at fo ur theoretical levels [HF, B3LYP, MP2, and MP2(full)] using three different basis sets. The most rigorous method employed was Moller-Plesset second or der perturbation with valence plus core electron correlation using 183 basi s functions for the calcium-neon complexes and 187 basis functions for the calcium-argon complexes. Correcting the dissociation energies, bond distanc es, and frequencies for basis set superposition error (BSSE) were done at t he most rigorous level of theory by fitting the Morse function to the poten tial energy curves generated by the counterpoise procedure. At this level o f theory, proceeding from the neutral to the doubly charged complexes, the calcium-neon bond distances range from 5.40 to 2.45 Angstrom with dissociat ion energies (De) from 0.03 to 5.86 kcal/mol. Likewise, the calcium-argon b ond distances range from 5.00 to 2.70 Angstrom with dissociation energies f rom 0.23 to 16.80 kcal/mol as the metal charge increases. Good theoretical agreement is obtained with experimental data when available, while the rema ining results can aid in the interpretation of future experiments. In all c omparable cases where the calcium-rare gas complexes possess equivalent cha rge, the argon atom is bound tighter to the metal than the neon atom due to its larger atomic polarizability. An examination of the relationship betwe en dispersion and charge-induced dipole forces is done using these calcium- rare gas complexes. (C) 2000 American Institute of Physics. [S0021-9606(00) 30823-6].