Ab initio study of the second virial coefficient protein — protein on the basis of intermolecular potential energy surface

Intermolecular potential energy surface (IPS) for protein — protein has been examined using RHF, DFT-B3LYPand MP2 levels of theory with 6-31G, 6-31G* basis sets. A number of basis sets were used in order to evaluatethe basis set effects, at all three levels of theory, basis sets has significant effects on the calculated potentialenergy curves (including position, depth and width of the potential well). Counterpoise (CP) correction has beenused to show the extent of the basis set superposition error (BSSE) on the potential energy curves obtained forprotein — protein system. The deepest BSSE-corrected potential well have been obtained at B3LYP level oftheory with 6-31G basis set. The second virial coefficients calculated this way are fitted to the initial coefficientsB2 varying E and ro, eventually some other parameters.