How to compute BSSE

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For a definition please look at: basis set superposition error (BSSE)

Gas phase

To compute the basis set superposition error (BSSE) in gas phase you can use the Counterpoise keyword. Check the example BSSE_gasphase.in. Fragments can be specified in GaussView through the Edit -> Atom groups commands.

Solvent

This keyword does not work for species in solution, as SCRF and Counterpoise can not be used together. The way to estimate the BSSE in gas phase can not be directly applied to solution, as in solution the cavity also has an important role. The way we have found to sort out this is do the following calculations for the species in solution:

• 1(2nb) The fragment 1, with ghost atoms of fragment 2 with no basis sets on 2 (example BSSE_solv_nobasis.in)
• 2(1nb) The fragment 2, with ghost atoms of fragment 1 with no basis sets on 1
• 1(2wb) The fragment 1, with ghost atoms of fragment 2 with basis sets (example BSSE_solv_withbasis.in)
• 2(1wb) The fragment 2, with ghost atoms of fragment 1 with basis sets

The BSSE correction is: 1(2nb) - 1(2wb) + 2(1nb) - 2(1wb)