Calculation of second virial coefficients of alkanes with the MM2 and MM3 force fields

Abstract

The second virial coefficients, B(T), of n-butane and n-octane have been calculated by means of a Monte Carlo method for two popular all-atom force fields, MM2 and MM3. To bring the predicted B(T) values into line with experiment, a rigorous procedure has been used to reparametrize the non-bonded parameters in the two force fields. The procedure fits the parameters simultaneously to high quality methane dimer energies and experimental methane second virial coefficients. The n-alkane B(T) values predicted by the new force fields are in good agreement with experiment. The effect of the torsional potential on the calculated virial coefficients has also been examined.