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I study reaction A + B → C + D in a water using DFT. I think I should apply some kind of correction over RRHO because it is not true in a solvent. I found the given work (https://doi.org/10.1021/jp980229p) and got to the point of calculating that p=1358 atmospheres... How could I now apply it for Gibbs free energies / reaction barriers? Best

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  • $\begingroup$ The answers on mattermodeling.stackexchange.com/questions/10249/… can help? $\endgroup$
    – Andrea Pellegrini
    Feb 21 at 10:52
  • $\begingroup$ This leads to the computations on solvation free energy. I seek on how to apply correction to translational entropy for the solvated systems already. Gaussian, by default, assume 1 atmosphere pressure what is nonsense for a liquid such as water which as it actually 1358 times greater... $\endgroup$
    – farmaceut
    Feb 21 at 11:59

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You can set the pressure (and temperature) for thermochemistry calculations in Gaussian: https://gaussian.com/pressure/

If you want to calculate manually from the partition function, see section 2.1 of Gaussian's Thermochemistry writeup: https://gaussian.com/wp-content/uploads/dl/thermo.pdf

I'll reproduce the two equations needed here: $$ q_{trans}=(2\pi Rm/h^2)^{3/2}(RT/P) $$ Note that the above is the same as equation 16 in the Martin paper linked. $$ S_{trans}=R(lnq_{trans}+3/2) $$

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