<div dir="ltr"><div class="gmail_default" style="font-size:small">Dear Xavier and Jurg,</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">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.</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">By the way, any plan to implement GFN2-xTB in CP2K?</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Regards,</div><div class="gmail_default" style="font-size:small">Pierre</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Apr 6, 2022 at 9:50 AM Jürg Hutter <<a href="mailto:hutter@chem.uzh.ch">hutter@chem.uzh.ch</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi<br>
<br>
yes, this looks bad. I cannot see an obvious problem with your input. But as you have the<br>
two codes side by side, why don't you start with comparing energies, forces and stress<br>
at the initial geometry?<br>
CP2K prints individual energy components and it should be possible to compare with<br>
the DFTB+ output.<br>
<br>
regards<br>
<br>
Juerg Hutter<br>
<br>
________________________________________<br>
From: <a href="mailto:cp2k@googlegroups.com" target="_blank">cp2k@googlegroups.com</a> <<a href="mailto:cp2k@googlegroups.com" target="_blank">cp2k@googlegroups.com</a>> on behalf of Xavier Bidault <<a href="mailto:jazzquark@gmail.com" target="_blank">jazzquark@gmail.com</a>><br>
Sent: Tuesday, April 5, 2022 10:22 PM<br>
To: cp2k<br>
Subject: [CP2K:16807] xTB descrepancy between CP2K and DFTB+<br>
<br>
Hello,<br>
<br>
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:<br>
1950.83 A3 with DFTB+<br>
1759.92 A3 with CP2K<br>
<br>
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:<br>
1467.79 A3 with DFTB+<br>
1467.14 A3 with CP2K<br>
So, DFTB + D3(0) is consistent between CP2K and DFTB+, but not GFN1-xTB.<br>
<br>
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?<br>
<br>
I attached the CP2K input file for the GFN1-xTB calculation.<br>
<br>
Please, let me know.<br>
<br>
Thank you,<br>
Xavier<br>
<br>
<br>
<br>
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