[CP2K-user] [CP2K:22074] DFTB3 D3(BJ) GAMMA

[Jürg Hutter]

Hi

1) and 2) Have a look in "tests/DFTB/regtest-vdw" . There you find some examples on how to use D3 with DFTB.
3) The D3(BJ) parameters have to be given in the input file. The data file only contains the atom specific parameters,
    not the method parameters.
4) Yes, this is the DFTB3 parameter. I don't know if CP2K can read the parameter from the DFTB parameter file. I would have to check.
5) You need the keyword. According to the manual the default is not to use it.
6) I cannot answer this question.

regards
JH

________________________________________
From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Dobromir A Kalchevski <dobromirak at gmail.com>
Sent: Saturday, January 31, 2026 11:21 AM
To: cp2k
Subject: [CP2K:22073] DFTB3 D3(BJ) GAMMA

Hello valued developers and users,

I am trying to setup DFTB3 with D3 correction and GAMMA damping and I can't find the answers to all of my questions in the forum threads. Also some answers are not completely clear to me.

1) If I am to use the D3 correction - is it enough to include
          DISPERSION_TYPE D3(BJ)
          DISPERSION_PARAMETER_FILE ${LIBPATH}/dftd3.dat

or should I also include the &VDW_POTENTIAL section and where if I am not using DFT (&XC section)

2) does D3(BJ) work with DFTB3 or does only D3 work

3) are both the D3 and the D3(BJ) parameters in the dft3d.dat file. If not - for D3(BJ) I can find only a1, a2 and s8, but I can't find anywhere the fourth one. Why are the default values set to 0

4) is the keyword DFTB3_PARAM in KIND the Hubbard parameter and is it necessary. The 3ob .skf files technically include it, basically does CP2K read it from the .skfs.

5) is using 3ob enough for DFTB3 or do I have to include the keyword DIAGONAL_DFTB3 in &DFTB

6) if HB_SR_GAMMA is the GAMMA damping for hydrogen bonds, is its use recommended for general organics at the moment or it would rather worsen the results, as before

I am attaching an example input file for QM/MM Metadynamics.

Best Regards,
Dobromir



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