[DFTB-Plus-User] Number of external charges in DFTB+

[Bálint Aradi]

Dear Ben,

> I want to calculate a molecular system in presence of an electrostatic field. 
> The electrostatic field consists of more than 20,000 atoms and when I run 
> DFTB+ there is an segemtation fault. 
> 
> I think there has to be a limit for external charges, since it works perfectly 
> with only a few external charges.

  Theoretically (!) there is no limit for the number of external
charges. Practically, there could be one, especially if using the Intel
compiler for compilation:

  If some arithmetic expression in the code uses the matrix of the
charges, then a temporary product is created during evaluation. If it
exceeds the stack size (which is per default 8 MB in bash/tcsh), then a
segmentation fault occurs in the ifort compiled binaries. Could you try
to set the maximal stack size in your shell to unlimited and try it again?

  bash: ulimit -s unlimited
  tcsh: limit stacksize unlimited

Please check if those settings solve the problem. Should it be not the
case, please just send me your input (including geometry and SK-files)
as a tgz archive, so that I can try to reproduce the case.

  Best regards,

    Bálint


Ps. I carbon copied your email to the DFTB+ User list. Please in the
future post questions regarding the use of DFTB+ to that list, so that
also other people can profit from the discussion.

-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/en/~b_aradi


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