Thermodynamic Corrections

With the xtb thermo submodule, thermodynamic properties of a structure can be evaluated based on a previously calculated Hessian. The mRRHO approximation is used for these calculations. It can be invoked with:

xtb thermo [options] struc.xyz <hessian file>

With [options], the type of Hessian is defined, e.g., –orca or –turbomole. The output will display a total energy of 0 Hartree, with the sum of thermocorrections as total free energy, and include different components such as zero point energy, G(RRHO) w/o ZPVE, and G(RRHO) contrib.:

         :::::::::::::::::::::::::::::::::::::::::::::::::::::
         ::                  THERMODYNAMIC                  ::
         :::::::::::::::::::::::::::::::::::::::::::::::::::::
         :: total free energy           0.743903967832 Eh   ::
         ::.................................................::
         :: total energy                0.000000000000 Eh   ::
         :: zero point energy           0.826262177517 Eh   ::
         :: G(RRHO) w/o ZPVE           -0.082358209684 Eh   ::
         :: G(RRHO) contrib.            0.743903967832 Eh   ::
         :::::::::::::::::::::::::::::::::::::::::::::::::::::

The thermo submodule is especially useful, when evaluating different temperatures. The temperature can be set with the --temp <REAL> flag. For further details, refer to the documentation.