Thermo Submodule

Note

This feature is only present in version 6.3 and newer

The thermo submodule allows to evaluate thermodynamic functions from data produced in previous calculations, generally the results are equivalent to the ones produced in a frequency calculation in xtb.

To run the thermo submodule use

xtb thermo [options] <geometry> [hessian]

The geometry can be any format accepted by xtb, while the hessian format depends on the options passed to the thermo submodule. It defaults to the non-massweigthed, projected Turbomole hessian data group.

Possible options are:

--sthr REAL Rotor cutoff for RRHO partition function in rcm
--temp REAL Temperature for thermodynamic functions in K, takes a comma separated list of temperatures
--turbomole Read a Turbomole Hessian file, use this only when $nomw is not present in control
–dftb+
Read a DFTB+ hessian.out file, projection will be performed automatically

An example calculation is given here, reevaluating at a different rotor cutoff for multiple temperatures

xtb benzene.xyz --namespace benzene --ohess
...
xtb thermo --sthr 100 --temp 50,100,150,200,250,300 benzene.xtbopt.xyz benzene.hessian
...

Molecule has the following symmetry elements: (i) (C6) (C3) 7*(C2) (S6) (S3) 7*(sigma)
It seems to be the D6h point group
d6h symmetry found (for desy threshold:  0.10E+00) used in thermo

...

       T/K    H(0)-H(T)+PV         H(T)/Eh          T*S/Eh         G(T)/Eh
   ------------------------------------------------------------------------
     50.00    0.633464E-03    0.981387E-01    0.362609E-02    0.945126E-01
    100.00    0.128528E-02    0.987905E-01    0.815319E-02    0.906373E-01
    150.00    0.203561E-02    0.995409E-01    0.131373E-01    0.864036E-01
    200.00    0.296494E-02    0.100470E+00    0.185801E-01    0.818901E-01
    250.00    0.413423E-02    0.101639E+00    0.245239E-01    0.771156E-01
    300.00    0.558192E-02    0.103087E+00    0.310070E-01    0.720801E-01 (used)
   ------------------------------------------------------------------------

...