Abstract

The potential energy of Alanine-Methionine was studied on the basis of ab initio calculations performed by using the HF,DFT-B3LYP and MP2 methods with 6-31G and  6-31G* basis sets. The following trends with basis set can be deduced for the depth (D_e= -E_int (R_e) = -E_min) of the potential well of the calculated intermolecular potential energy surfaces (IPSs). In ab initio calculations the basis set superposition error (BSSE) is important. This error can be eliminated to some extent by using the counterpoise correction method (CPC). In this work, to estimate the interaction energy  in the system we use the Morse potential model, and we estimate adjustable parameters used in the Morse model and theoretically second virial coefficient for the system. To determine the second virial coefficients,  is used to obtained the model’s parameters over the range of temperatures of interest.

Key words: IPS, second virial coefficient, basis set superposition error, counterpoise correction method, MP2, HF and DFT-B3LYP method.