Is SAPT energy the hydrogen bond energy?

Hi, the hydrogen bond energy can be calculated by E_bond = E_dimer - E_monomer. I am not sure whether the structures of the dimer and the monomer should be optimized. It seems that SAPT can only use the same structure of dimer and monomer. I found that many articles use SAPT to decompose the hydrogen energy without details. I do not know how I should do that, only optimize the dimer energy?
Thanks!

“E_bond = E_dimer - E_monomer” isn’t true. That determines an interaction energy, which is going to include other effects than just the hydrogen-bond, like dipole interactions.

SAPT computations use an optimized dimer geometry and neglect effects from how the geometry changes from the isolated monomer to the monomer as part of the complex.

This seems like a good use case for functional group SAPT (F-SAPT). F-SAPT allows you to partition your system into chemically sensible functional groups and then estimates the contribution of those functional groups to the total dimer interaction energy.

The conformation of the system should be optimized to the dimer geometry. When choosing which atoms to put into the donor and acceptor functional groups, make sure that you include atoms adjacent to the heavy atom acceptor (atoms labeled B and BB in Figure 1 in this paper). The electronic properties of the acceptor are influenced by these atoms, especially for sp2 hybridized acceptors. Additionally, check the docc values in the “Orbital Check” section of the output from fsapt.py. If any value is bigger than 0.1, you’ve likely made a poor choice in partitioning your functional groups.

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