Vibration spectroscopy
Molecular modeling

This section presents the calculation of normal modes of vibration around their equilibrium position of atoms included in an atomistic model (isolated molecule or periodic model). The frequencies of these modes correspond to the mid- to far-infrared spectral range from roughly 4,000 to a few hundred cm ^–1 . In principle, prediction is possible for all accessible vibrational modes, whereas only those modes that obey the selection rules inherent in an experimental spectroscopic technique are observable by that technique.

Two approaches are possible:

• calculation of the force constant matrix in the harmonic approximation;

• calculation of the Fourier transform of the velocity autocorrelation function derived from a molecular dynamics simulation....