Fundamental absorption frequency from quasi-classical direct ab initio molecular dynamics: diatomic molecule

A new approach is proposed to extract the fundamental absorption frequency from classical molecular dynamics simulation in which the oscillator amplitude is specified by setting the total energy equal to the harmonic zero-point energy. This approach is applied to D2 molecule. The fundamental absorption frequency and the anharmonic constant of D2, obtained from the quasi-classical direct ab initio molecular dynamics simulation method with the full Configuration Interaction level of theory with the aug-cc-pVTZ basis set, compare well with the experimentally observed values.