We calculated vibrational spectra by means of a molecular dynamics simulation which utilizes intramolecular forces from ab initio molecular orbital calculations for instantaneous configurations of each molecule. Intermolecular interactions were determined with conventional force fields. Calculated molecular orbitals from the time-dependent, instantaneous molecular configurations were also used to evaluate dipole moment and partial charges. We examined the validity of the present approach by evaluating infrared spectra for liquid carbon dioxide and water. We could capture some important features of intramolecular vibrational spectra of molecular liquids by this method, albeit there is room for further improvement in the descriptions of intermolecular interactions, especially of hydrogen bond. Possible extensions for accurate intermolecular and intramolecular vibrational spectrum were discussed. © 2012 Wiley Periodicals, Inc.