[CP2K-user] [CP2K:16820] xTB descrepancy between CP2K and DFTB+

[Jürg Hutter]

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

Not in my group, but I'm sure somebody will do it.

regards

Juerg

________________________________________
From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Pierre-André Cazade <pierre.andre.cazade at gmail.com>
Sent: Wednesday, April 6, 2022 12:10 PM
To: cp2k at googlegroups.com
Subject: Re: [CP2K:16811] xTB descrepancy between CP2K and DFTB+

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<mailto: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<mailto:cp2k at googlegroups.com> <cp2k at googlegroups.com<mailto:cp2k at googlegroups.com>> on behalf of Xavier Bidault <jazzquark at gmail.com<mailto: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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