[CP2K-user] [CP2K:16811] xTB descrepancy between CP2K and DFTB+

[Pierre-André Cazade]

Dear Xavier and Jurg,

If I may join this discussion. I have recently started using TB methods,
both DFTB and xTB. I am currently testing these methods with CP2K, DFTB+,
and for xTB with xtb software. I am performing a MD simulation of a
chemical reaction. Both CP2K and xtb show a similar reaction path using xTB
but with DFTB+ the MD simulation explodes. However, if I use DFTB, the same
input is stable. Therefore, I wonder if the problem does not come from
DFTB+ rather than CP2K.

By the way, any plan to implement GFN2-xTB in CP2K?

Regards,
Pierre

On Wed, Apr 6, 2022 at 9:50 AM Jürg Hutter <hutter at chem.uzh.ch> wrote:

> Hi
>
> yes, this looks bad. I cannot see an obvious problem with your input. But
> as you have the
> two codes side by side, why don't you start with comparing energies,
> forces and stress
> at the initial geometry?
> CP2K prints individual energy components and it should be possible to
> compare with
> the DFTB+ output.
>
> regards
>
> Juerg Hutter
>
> ________________________________________
> From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Xavier
> Bidault <jazzquark at gmail.com>
> Sent: Tuesday, April 5, 2022 10:22 PM
> To: cp2k
> Subject: [CP2K:16807] xTB descrepancy  between CP2K and DFTB+
>
> Hello,
>
> I run a variable-cell optimization of a high-energy molecular crystal,
> beta-HMX, with CP2K 9.1 and DFTB+ 21.2, both using GFN1-xTB, which includes
> D3(BJ) correction. To compare apples to apples, I optimized the same
> supercell, using the Gamma point. The initial (experimental) volume for the
> supercell is 2069.80 A3. The resulting volume is:
> 1950.83 A3 with DFTB+
> 1759.92 A3 with CP2K
>
> In order to check if I did something wrong in the configuration files, I
> used DFTB + D3(0) with the default DFTB parameter file from CP2K for both
> CP2K and DFTB+, and I find:
> 1467.79 A3 with DFTB+
> 1467.14 A3 with CP2K
> So, DFTB + D3(0) is consistent between CP2K and DFTB+, but not GFN1-xTB.
>
> IMO, the dispersion correction of xTB is wrong somewhere in CP2K. Looking
> at the difference between CP2K and DFTB+, could it be that D3(BJ)
> correction is counted twice in CP2K? Or with some wrong units we don't have
> access to?
>
> I attached the CP2K input file for the GFN1-xTB calculation.
>
> Please, let me know.
>
> Thank you,
> Xavier
>
>
>
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