[DFTB-Plus-User] SCC does not converge.

[Ben Hourahine]

Hello Dawid,

have you tried a finite electronic temperature (this can really help
with self consistency)?
The attached example was at 0 Kelvin, I'd suggest something like room
temperature as a first test.

Also the SCC tollerance you are using is quite small (try the default
value, unless there is a good reason otherwise).

Regards

Ben

On 07/02/16 21:11, Dawid Grabarek wrote:
> Dear DFTB+ Experts,
>
> I want to perform geometry optimization of a system consisting of
> increasing
> number of amino acid residues.
> I have managed to successfully perform optimization for system up to
> 1870 atoms, using non-SCC DFTB approach.
> However when I want to use SCC-DFTB3 for system larger than 460 atoms,
> the charges do not converge even after a few thousand iterations. The
> iteration
> does not proceed in fact.
> I attach part of my output file:
>
>  9976   -0.21529827E+03   -0.13123659E+02    0.53106709E+01
>  9977   -0.17459612E+03    0.40702148E+02    0.53210677E+01
>  9978   -0.20103686E+03   -0.26440744E+02    0.53230816E+01
>  9979   -0.24096058E+03   -0.39923717E+02    0.53269557E+01
>  9980   -0.19704089E+03    0.43919692E+02    0.53385778E+01
>  9981   -0.21818849E+03   -0.21147597E+02    0.53345550E+01
>  9982   -0.25301554E+03   -0.34827052E+02    0.53358740E+01
>  9983   -0.27482831E+03   -0.21812768E+02    0.53316452E+01
>  9984   -0.29608303E+03   -0.21254728E+02    0.53454981E+01
>  9985   -0.26626843E+03    0.29814602E+02    0.53557124E+01
>  9986   -0.29473653E+03   -0.28468098E+02    0.53569507E+01
>  9987   -0.25516950E+03    0.39567029E+02    0.53763278E+01
>  9988   -0.28536057E+03   -0.30191072E+02    0.53798582E+01
>  9989   -0.28895556E+03   -0.35949882E+01    0.53806192E+01
>  9990   -0.22896112E+03    0.59994443E+02    0.53836906E+01
>  9991   -0.22485550E+03    0.41056157E+01    0.53812648E+01
>  9992   -0.22164301E+03    0.32124948E+01    0.53759401E+01
>  9993   -0.16929036E+03    0.52352651E+02    0.53873225E+01
>  9994   -0.19352833E+03   -0.24237970E+02    0.53825003E+01
>  9995   -0.16294863E+03    0.30579698E+02    0.53834931E+01
>  9996   -0.11288863E+03    0.50060003E+02    0.53970748E+01
>  9997   -0.10136437E+03    0.11524262E+02    0.53984882E+01
>  9998   -0.10537121E+03   -0.40068449E+01    0.53984460E+01
>  9999   -0.84099319E+02    0.21271891E+02    0.53857706E+01
> 10000   -0.76159647E+02    0.79396717E+01    0.53785016E+01
>  
>  Total Energy:                     -66.7997002259 H
>  Total Mermin free energy:         -66.7997002259 H
> ERROR!
> -> SCC is NOT converged, maximal SCC iterations exceeded
>
> I know that going up to 10 000 is crazy but just wanted to see what
> will happen.
>
> Anyway, I also attach two input files for systems for which I cannot
> reach the SCC convergence. What is more I also attach a PDF file which
> contains
> various parameters combination that I used to check whether changing
> parameters and Mixer will allow to reach convergence.
> I did that based on what I read in paper by V. Eyert (Journal of
> Computational Physics, 124, 271-285, 1996).
>
> Best wishes,
>
> Dawid Grabarek
>
>
>
> -------
> Dawid Grabarek, M.Sc.
> Wroclaw University of Technology
> Faculty of Chemistry
> Advanced Materials Modelling and Engineering Group
>
>
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-- 
      Dr. B. Hourahine, SUPA, Department of Physics,
    University of Strathclyde, John Anderson Building,
            107 Rottenrow, Glasgow G4 0NG, UK.
    +44 141 548 2325, benjamin.hourahine at strath.ac.uk

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