[DFTB-Plus-User] problems with a single point calculation

[natalia bedoya]

Dear All,

We are facing a particular problem trying to do a single point calculation.

 From a relaxed structure we do a very tiny displacement of one single 
atom in the system (0.01 Angstoms), and submit a single point 
calculation to get the forces  on the atoms caused by the displacement. 
   The calculation starts correctly but after the third step (sometimes 
second or first) during the SC loop the calculation gets stuck. The 
calculation does not die, but does not produce either any more data. We 
basically have to kill it because there is no outcome.

We use very often this approach in order to calculate the phonon 
spectrum from finite differences, and  it is the first time we get this 
kind of problem. What is curious is that for other displacements every 
thing works correctly. Moreover, depending on the amplitude of the 
displacement the problem appears for different displacements (i.e. for 
configurations for which another atom is displaced).

We have try to start a relaxation calculation by using one of the 
problematic configurations and we get the same problem.

Has somebody ever experienced something similar?

  We  appreciate any idea to overcome the problem!

Thanks!

Regards,

Natalia

-- 
Dr. Natalia Bedoya
Institute of Solid State Physics
Graz University of Technology
Petersgasse 16, 8010 Graz, AUSTRIA
Tel: +43 316 873 8465
Fax: -108475


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