47.8 Thermodynamical properties (THERMO)

It is also possible to calculate the thermodynamical properties of the molecule. Since MOLPRO can only handle Abelian point groups it is necessary to give the point group of the molecule in the input file:

THERMO,[SYM=pointgroup],[TEMP=value], [PRESS=value], [TMIN=value, TMAX=value, TSTEP=value]

pointgroup has to be the Schoenflies Symbol (e.g. C3v for ammonia; linear molecules have to be C*v or D*h respectively). If no point group is given, the point group is determined automatically, but only Abelian groups (D2H and subgroups) are recognized. If the molecule has higher symmetry this may eventually cause deviations in the rotational entropy.

The temperature (in K), pressure (in atm) or a range of temperatures (in K) can be given as options.

If no temperature or pressure is specified the zero-point vibrational energy and the enthalpy $H(T)-H(0)$ [kJ/mol], heat capacity $C_v$ [J/mol K] and entropy $S$ [J/mol K] are calculated for standard temperature and pressure ($T=298.150$ [K], $p=1$ [atm]).

The FREQUENCIES program sets the variable ZPE containing the zero-point-energy of the harmonic vibrations in atomic units. If the THERMO option is used, the variables HTOTAL and GTOTAL, containing the enthalpy and the free enthalpy of the system in atomic units, are also set.

molpro@molpro.net 2019-07-16