[DFTB-Plus-User] Problem with geometry optimization

[Bálint Aradi]

Dear Pasan,

your system is basically a metallic surface, therefore, it needs an 
electronic temperature to achieve proper convergence. Setting

   Filling = MethfesselPaxton {
     Temperature [K] = 1000
    }

should work.

Two more remarks:

* You could speed up the calculation somewhat by using the MPI-parallel 
version of the code, and the ELPA solver and processor groups (see the 
manual).

* Your k-point sampling is unbiased. The cell is very large along a1 and 
a3, but short along a2, therefore, you it should be enough to use one 
k-point along b1 and b3, and 2 or 4 along b2.

Best regards,

Bálint



On 16.01.22 13:12, Pasan Henadeera wrote:
> Dear developers and users,
> 
> I have been trying to use DFTB+ to optimise a structure made of Si 
> (consisting of around 750 atoms). However, even though I reduce the SCC 
> tolerance and increase the Max steps, I still am unable to figure out 
> how convergence can be obtained. Would it please be possible to give me 
> some guidance regarding this matter? I have attached the input and log 
> files as well. The optimization and Hamiltonian sections of the input 
> are as follows,
> 
> 
> Driver = GeometryOptimization {
> Optimizer = Rational {DiagLimit = 1.0e-2}
> LatticeOpt = Yes
> MaxSteps = 500
> }
> 
> Hamiltonian = DFTB {
>    Scc = Yes
>    SccTolerance = 0.2
>    SlaterKosterFiles = Type2FileNames {
>      Prefix = "../../../../slakos/wfc/"
>      Separator = "-"
>      Suffix = ".skf"
>    }
>      MaxAngularMomentum {
>      Si = "d"
>    }
>    KPointsAndWeights = SupercellFolding {
>      1 0 0
>      0 2 0
>      0 0 2
>      0.5 0.5 0.5
>    }
> }
> 
> ParserOptions {
>    ParserVersion = 7
> }
> 
> 
> 
> I have only 16GB of memory, which is why I tried reducing the number of 
> k-points. However I got the same issue when using more k-points.
> 
> 
> Thank you
> -- 
> Best regards
> Pasan Henadeera
> 
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> 


-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b-aradi/


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