# Gibbs Free Energy for solvation using Gaussian09

I am trying to compute the $$\Delta G$$ for the solvation of a molecule using the continuum dielectric model in Gaussian09. Following the recomendation in the manual of the software, I am using the SMD (solvation model based on density), but I am haveing difficulty to interpret the output. This is the comand line I am using

#P MP2/6-311++G** SCRF(SMD,Solvent=Acetonitrile)

In SMD, the Gibbs free energy is divided in two terms

$$G_{sol} = G_{EP} + G_{CDS},$$

where $$G_{EP}$$ is the bulk-electrostatic contribution arising from a SCRF treatment and $$G_{CDS}$$ is the contribution arising from short-range interactions between the solute and solvent molecules in the first solvation shell. In the Gaussian output, there is the following

Error on total polarization charges =  0.04321
SCF Done:  E(UHF) =  -263.928410150     A.U. after   22 cycles
NFock= 22  Conv=0.84D-08     -V/T= 2.0012
<Sx>= 0.0000 <Sy>= 0.0000 <Sz>= 0.5000 <S**2>= 0.8777 S= 0.5619
<L.S>= 0.000000000000E+00
KE= 2.636170281119D+02 PE=-1.036154210633D+03 EE= 3.034189165458D+02
SMD-CDS (non-electrostatic) energy       (kcal/mol) =       1.57
(included in total energy above)

and

E(PUHF)=      -0.26394237020D+03        E(PMP2)=      -0.26487244445D+03

I can identify what is $$G_{SMD}$$ (1.57 kcal/mol in this case), but I don't know what is the $$G_{EP}$$ contribution. would it be the E(PMP2)? Or Gaussian is not computing this?

• Usually Gaussian gives you the total energies. So E(PMP2) is what you need. However, you're missing the freq stuff so that value won't help you at all. Do a gp opt then freq and do the same with the solvent. Subtract. There's a white paper on thermochemistry you might want to enjoy. Commented Aug 26, 2023 at 0:55