Dear all,
I want to compare the reactivity of two diastereomers in a reaction, and therefore I'd like to calculate the activation energies of two compounds in a rate-limiting step. I've optimized the reactants and the products (B3LYP, 6-31g(d,p)/LANL2DZ, Grimmie D3), located the transition state (QST2), and then confirmed the transition state with IRC calculation. All the calculations have been done in a gas phase. Now, I would like to find the reactant, transition state and the product energies in a solution (dichloroethane) with M06, 6-311++G**/SDD level of theory.
How should I do this? Do I need now just to run the SP calculations with this level of theory and with scrf=(iefpcm,solvent=dichloroethane) keyword? Or should I reoptimize the structures with the previously mentioned level of theory with a solvent, and then do a SP calculation with M06? Which energies should I use in the end for making a figure of a reaction coordinate? Just the output energies from the summary file or something else?
Thanks in advance for your help!
No. You should reoptimze everything in the solvent and recalculate the SP energies.
Then you can compute your DH, DG, and DS and make your plots
I have well explained these calculations on my papers
Please take a look
https://scholar.google.com.eg/citations?user=YMWwJ_QAAAAJ&hl=en
Dear Uros Stojiljkovic ,
As dichloroethane is a pretty non-polar solvent (Eps = 10.125), then you can assume that the geometries will not differ substantially in solution with respect to those in gas-phase. Therefore, it should be fine if you just do single-point energy calculations on top of the gas-phase-optimized structures. Instead of the IEFPCM model, as you may want to calculate thermodynamic values (enthalpies, Gibbs free energies...), my recommendation is that you use the SMD one.
Be aware that, if you want the delta-H / delta-G, you need to calculate the frequencies in gas-phase, and then add the corresponding thermal corrections to enthalpy / Gibbs free energies to the electronic energies in solvation.
Hope you find it helpful
Dear Enrique Manuel Arpa ,
Thank you sincerely for your answer! Your insight was very helpful and solved my problem. Thank you for that!
Cheers,
Uros
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