CALCULATIONS OF VIBRATIONAL SPECTRA AND THERMAL PROPERTIES OF METHANE SERIES BY DENSITY FUNCTIONAL THEORY(DFT)

The density functional theory calculations using B3' exchange and Lee Yang Parr's correlation functional (B3LYP) with 6 31G  basis set are carried out to study and optimize equilibrium structure and fundamental vibrational frequencies in the equilibrium for CH 4, CH 3D, CH 2D 2, CHD 3, and CD 4. The relative error ranges from 1.1% to 6.3% between the calculation and the observation values of fundamental vibrational frequencies. After scaled, the relative error ranges from 0.1% to 2.9%. With the increase of deteurium substituted atom numbers in methane, entropy and heat capacity increase while total energy and enthalpy decrease.