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I have been exploring xtb and used it to run docking on an ion pair. I get the message at the end in the .log file. The xyz files of input structures were obtained from Gaussian output files. Is there a way to optimize monomers using xtb before submission so that the interaction energies output are deemed physical? I am unsure of how to solve this issue. All advice is highly appreciated.

Thank you,


 Interaction energies
 Attention: monomers are not optimized
 Interaction energies are not physical
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  • $\begingroup$ I think that the docking module should be used only to have starting structures for further complex optimization. $\endgroup$
    – Camps
    Commented Jun 12, 2023 at 13:43
  • $\begingroup$ Thanks! That's my goal as well – however, I was not sure if there's something that I am missing in terms of using xtb. $\endgroup$
    – bhopshang
    Commented Jun 12, 2023 at 16:58

1 Answer 1

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The error message states

Interaction energies

Attention: monomers are not optimized

Interaction energies are not physical

This suggests that the interaction energy is computed as E(interaction) = E(aggregate) - sum[E(monomer)]. The true interaction energy is the difference of the optimized aggregate to the optimized monomers. Looking into the source code, this warning arises at

https://github.com/grimme-lab/xtb/blob/0e66cab758133bcaa6ea2bb59012a1603166e6fd/src/docking/search_nci.f90#L964

The warning appears to be issued always, suggesting that it is just to inform you that the interaction energy estimates are not accurate.

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