[CP2K-user] [CP2K:17604] Large discrepancy in xTB results from CP2K vs DFTB+

[Anton Lytvynenko]

Dear Magnus,

but do you have any reasons to expect that these methods must yield 
similar results? They are different and both are not so precise for the 
systems with complicated electronic effects.

Yours,

Anton

01.09.2022 12:48, Magnus Rahm пише:
> Dear all,
>
> I want to use CP2K (version 8.2, trying to get a more recent version 
> compiled) together with xTB for a crystal containing Li and O. I get 
> strange results already for a simple LiO2 crystal:
>
> * There is a very large discrepancy compared to DFTB+ (version 22.1).
> * Mulliken charges tend to be large, meaning that CHECK_ATOMIC_CHARGES 
> stops the SCF. If I turn it off, the system tends to converge 
> systematically to values just outside the "chemical range". Mulliken 
> charges obtained by DFTB+ are significantly smaller (and within 
> "chemical range").
> * The energy-volume curve looks strange and very different from DFTB+.
>
> I have tried converging with respect to system size and the EWALD / 
> ALPHA and GMAX parameters, but they have only a marginal impact. I 
> have tried similar calculations for a number of periodic systems. 
> Sometimes I get agreement, sometimes not. I also tried calculations 
> for CO and NO molecules which agree perfectly between CP2K and DFTB+, 
> whereas an artificial LiF molecule does not.
>
> A perhaps related issue was reported in 
> https://groups.google.com/g/cp2k/c/oFwgGcQuySs but the solutions 
> suggested there did not solve my problem.
>
> I attach input scripts for CP2K and DFTB+, as well as a figure showing 
> the E-V curve for LiO2 obtained with CP2K and DFTB+. I'm new to CP2K, 
> DFTB+ and xTB so I suspect I have made some simple mistake, and any 
> advice is appreciated.
>
> Kind regards,
> Magnus Rahm
>
>
>
>
>
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