I am looking for a method to estimate the contribution from Pauli repulsion to the interaction energy of a molecular dimer in an electronic structure computation (e.g. with Density Functional Theory). I'm aware of SAPT and SAPT(DFT) decomposition schemes, but as far as I understand, these estimate the contribution from the exchange interaction (amongst other contributions), which contains both Pauli repulsion and covalent bonding. Are there other energy decomposition schemes (or other methods in general) that can estimate the purely repulsive part of the exchange interaction?
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2 Answers
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I'm honestly not overly familiar with these schemes, but I believe the ADF package has a bonding energy decomposition scheme by Ziegler and Rauk implemented in it, and there's also the Morokuma scheme which looks to be available in at least GAMESS and ADF. I think these both produce the terms you're looking for.
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I found an energy decomposition scheme that does exactly what I was looking for. Here is a link to a paper describing the scheme:
http://dx.doi.org/10.1063/1.3253797
The sum of the repulsive and electrostatic contribution to the interaction energy of a dimer is defined as the difference in energy between the dimer and the two separate monomers, where the electron density of the dimer is constrained to be the sum of the monomer densities. This paper shows that this energy can be computed variationally in the context of Kohn-Sham DFT. The electrostatic interaction is easily identified, and the residual can be attributed to Pauli repulsion.