Process Thermochemistry Tool
The Process Thermochemistry tool calculate thermal corrections to electronic energy. This requires a structure with an associated energy and/or frequency information (i.e Gaussian, ORCA, or Psi4 output). Multiple conformers can be grouped together to calculate relative energies. Thermochemistry information can be exported by saving to a file or copying directly to the clipboard in CSV format.
The quasi-RRHO free energy from Grimme and the quasi-harmonic free energy from Truhlar et. al. can both be used to mitigate errors in vibration frequencies. In short, quasi-RRHO uses a damping function on the entropy contribution of frequencies, and the entropy is supplemented with free rotor entropy. Modes with frequencies below ω0 are dampened much more than those above. Quasi-harmonic treats all frequencies below ω0 as ω0.
The energy of each conformer group is calculated using the partition function of the conformer ensemble:
where is the energy (i.e. electronic energy, enthalpy, free energy, etc.) of the ith conformer, and
is the ensemble energy (i.e. electronic energy, etc.) for the jth molecule group. The energies of the reference group and the "other" group are the sum of the energies of their ensembles':
ZPE is the RRHO enthalpy at 0 K.