A New ab Initio Based Model Potential for Methane

We present a model potential for methane based on BSSE corrected MP3 level interaction energies of 132 methane dimers using the aug(df,pd)-6-311G^** basis set (6-311G^** basis set augmented with diffuse d and f functions on carbon atoms and diffuse p and d functions on hydrogen atoms). The density, heat of evaporation and self-diffusion coefficient of liquid methane obtained by an MD simulation using the model potential reproduced the experimental values considerably better than the previous model potential based on MP3/6-311G(3d,3p) level interaction energies.

Table 1 Destiny, Heat of Evaporation and Self-Diffusion Coefficient of Liquid Methane Obtained by Molecular Dynamics Simulations^a.

                                                                             
Param            Density      Heat of Evaporation     Self-Diffusion Coeff
                                                                             
Tsuzuki(1994)    0.378 (-11%)    1.66 (-15%)            6.0  (+11%)
This Work        0.406 (-4%)     1.92 (-2%)             5.3  (-2%)
Exp.             0.424           1.96                   5.4
                                                                             
aDensity in g cm-3, heat of evaporation in kcal mol-1, and self-diffusion coefficient in 10-9 m2 s-1