Isolate dispersion contribution in vdW-DF2 calculations
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Michael Fischer
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Oct 13, 2023, 4:16:20 AM10/13/23
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Dear all,
I am studying host-guest systems (molecules in zeolites) with the rev-vdW-DF2 functional (X_B86_R, PW92 correlation, LMKLL dispersion) and I am looking at the possibility to calculate the dispersion contribution to the total interaction energy.
In the past, I have used Grimme-type dispersion correction, e.g., PBE-D3. Here, it was fairly trivial to calculate the dispersion contribution as: E_disp = E_disp(host+guest) - E_disp(host) - E_disp(guest) ...where the E_disp terms on the right-hand side correspond to the energy values given in the line "Dispersion energy" in the CP2K output.
With rev-vdW-DF2, "Dispersion energy" is also printed. However, what is notable in the first place is that the dispersion energy is always positive. A subtraction as in the above equation gives results that look plausible at first, but a comparison to the total interaction energies shows that the E_disp contribution is sometimes more negative than E_tot, something which seems implausible.
Is there some way to isolate the dispersion contribution in calculations using non-local vdW-DF approximations?
Any suggestion will be highly appreciated! Thank you and best regards, Michael
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Jürg Hutter
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Oct 16, 2023, 5:08:42 AM10/16/23
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Hi
the printed dispersion energy is the calculated energy of the non-local
vdW energy functional (only the non-local part!). Together with the XC
energy you get the full functional energy. No other information is available.
regards
JH
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From: cp...@googlegroups.com <cp...@googlegroups.com> on behalf of Michael Fischer <doktor...@gmail.com>
Sent: Friday, October 13, 2023 10:16 AM
To: cp2k
Subject: [CP2K:19362] Isolate dispersion contribution in vdW-DF2 calculations
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Dear Prof. Hutter,
Thank you very much for the clarification. I presume that it cannot be expected that a simple "switching off" of the dispersion part (commenting out the entire vdW_POTENTIAL block and re-running a single-point calculation with the same combination of exchange and correlation functionals) would not give a physically meaningful estimation of the dispersion contribution (as the difference between "full" rev-vdW-DF2 energy and the "exchange-corellation only" energy), because some part of the local contribution is implicitly included in the exchange-correlation part. Or could that be a plausible option?
Thanks again, best regards, Michael
Jürg Hutter
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Oct 16, 2023, 5:28:33 AM10/16/23
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Hi
I cannot answer this question. I would suggest to check the papers where
these functionals have been proposed.