CCL: BSSE Counterpoise correction
- From: "Lee Jones"
- Subject: CCL: BSSE Counterpoise correction
- Date: Fri, 28 Jun 2019 08:05:10 -0400
Sent to CCL by: "Lee Jones" [bunglinpie|,|googlemail.com]
Hi. I'm after a little guidance regarding Basis Set Superposition Error.
I understand what BSSE is and how to perform a counterpoise correction
using ghost atoms, but my question is a little more fundamental.
Considering a bimolecular addition reaction where you have reactants A
and B that proceed to form a single molecule AB via a transition state
AB*, what species do you actually perform the CP correction on?
I read the following article which contains the following passage:
"This correction will depend on the geometries of the reactants. When
they are very far from one another, it will be very small: they don't
influence one another. When they are very close, this effect will be
small, for the same reasoning. It's the intermediate distances that have
the largest BSSE. These are the distances at or approaching the
transition state, which serves as the bottleneck for the reaction. If you
are not accounting for the artificial improvement near the transition
state, then you will get an incorrect approximation of the activation
energy, the energy difference between this transition state and the
This seems to suggest that, to a first approximation, I would only need
to CP correct the transition state AB* and can effectively ignore BSSE
for the reactants A and B at infinite distance and for the final product
AB (i.e. the BSSE only has a small effect on the overall reaction
energy/enthalpy) is this correct.