This is an example of the minimum input required to fit vibrational frequency data. Defaults are PHAS=G, TMIN=300, TMAX=6000, and LINR=No
(from the fact of more than one VIBE), but keywords may be used to supersede the defaults.
This method is provided for use in cases where little or no information is available in the literature about the molecule of interest. It contains a number of approximations:
Translational contributions to the heat capacity are treated classically via the equipartition function. This is generally a good assumption.
Rotational contributions to the heat capacity are treated classically via the equipartition function. This is a good assumption for most molecules at higher temperatures.
Hindered internal rotors are not explicitly treated, but rather approximated as vibrations. This is a less-good approximation.
In all cases, these approximations are more likely to break down at lower temperatures.
Figure 7.10: VIBE Input File
SPEC SIH2 ELEM SI 1 ELEM H 2 H298 58.0 S298 49.4 TEMP 1000 VIBE 999.83 VIBE 2011.69 VIBE 2001.72 END