Vibrational motion in molecules
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- Institutt for kjemi 
Zero-point vibrational corrections are carried out with analytical geometry and property derivatives at DFT level. This correction is obtained using a variation-perturbation approach, and is carried out around a variationally determined expansion point, denoted the effective geometry, leading to the inclusion of the anharmonicity of the potential. The corrections up to the second perturbation order are evaluated for the first time. The effective geometry, intermolecular frequencies, and intramolecular frequencies of the (H2O)2 dimer and the HOH-D2O dimer are calculated using the newly implemented analytical cubic force field at DFT level. The perturbation corrections implemented are evaluated for the dipole moment and polarizability of H2O, D2O, NH3, and CH4. Employing DFT, analytical geometry derivatives and property derivatives have been successful. The extra perturbation correction has been deemed significant for both the dipole moment and polarizability.