[CP2K-user] [CP2K:17599] Re: Large discrepancy in xTB results from CP2K vs DFTB+

[Magnus Rahm]

For the record, the problem is the same in CP2K version 2022.1.

On Thursday, September 1, 2022 at 12:48:35 PM UTC+2 Magnus Rahm wrote:

> 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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