How to study the solvent effect theoretically using gaussian 09 ?

aitouna

Dear everybody, how are you ?If we want to study the solvent effect of an organic reaction theoretically, what's the best approach to do it? Perform a single point energy of the optimized structures in the gas phase using solvent,
or repeat the optimization of the gas phase structures under solvent?


Sincerely,

elvisng

For studying organic reactions, both approaches have been used by researchers. If you just want to get an activation energy, the recommended approach is to do the optimization with solvent model, and this will only cost ~ 20-30 % more time. For relatively non-polar molecules, results will not be much different between the two approaches, but some picky reviewers will request you to do the optimizations always with solvent model. Therefore, just to play safe, you might want to optimize it with solvent model.

However, if you want to see more clearly how the solvent affects the relative reactivity between different pathways, then you might need to do calculations at both the gas phase and in solution phase, and compare the two activation energies. Therefore, it really depends on what you want to know about your organic reaction.

sobereva

Commonly, if the system is neutral and there is no local region showing highly ionic character, the result of geometry optimization performed in vacuum and in implicit solvation model is nearly indistinguishable.

Solvent effect has large impact on wavefunction and energy-related properties, such as dipole moment, electron density distribution, excitation energy, HOMO-LUMO gap, polarizability... For these properties, it is meaningful to study variation before and after employing solvation model.