[CP2K-user] [CP2K:16807] xTB descrepancy between CP2K and DFTB+

[Xavier Bidault]

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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