"Calculation of Vibrational Frequencies and Intensities"
James R. Cheeseman
Presenting author: James R. Cheeseman
Gaussian, Inc., 340 Quinnipiac Street, Bldg. 40, Wallingford, CT 06492, US
Molecular structure information provided by vibrational spectroscopy has to be extracted from a set of vibrational frequencies and corresponding intensities either by well established empirical rules, or by comparison to computed vibrational spectra. The ability to accurately compute vibrational frequencies and intensities, either absorption or scattered, has become an important addition to the field of vibrational spectroscopy. Well established model chemistries have led to the routine calculation of spectra. In addition to predicting the frequencies and intensities of spectral lines, calculations also provide the direction and magnitude of the nuclear displacement that occurs when a system absorbs a quantum of energy, which is useful in identifying and interpreting specific bands. Calculated spectra can be used as reference in the interpretation of spectra for which no reference experimental spectra are available. Structural descriptor models, based upon fitting of calculated spectra, can also provide insight into the expected biological and physical properties of a candidate molecule prior to actual synthesis. This talk will focus on the practical aspects of computing vibrational frequencies and intensities using the ab initio Density Functional Theory method of quantum chemistry. An overview of where the technology stands and what tools are currently available will also be presented.