Polarization response of methane encapsulated in water cages

The polarization effect of methane hydrates was investigated with first-principles calculations. The performances of various exchange-correlation functionals and basis sets used in the polarizability calculations for these non-bonded systems were carefully examined. M06-2X and CAM-B3LYP produce results similar with those at MP2 level. The total polarizability of methane hydrates is about the sum of those of methane and empty water cages. However, this does not mean a simple summation rule for the polarizability of methane hydrates. Further analysis reveals a reduced polarizability of encapsulated CH4 and an enhanced polarizability of water cage.