[CP2K-user] [CP2K:16809] xTB descrepancy between CP2K and DFTB+

[Jürg Hutter]

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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