[DFTB-Plus-User] Failure in diagonalisation

[Bálint Aradi]

Dear Zack,

On 05/18/2010 03:47 PM, Zack Terranova wrote:
> I understand that DFTB+ will fail with this error: "ERROR!
> -> Failure in diagonalisation routine zhegvd, non-positive definite overlap! Minor XXX responsible"
> when two atoms become too close together, or are on top of each other.  But why are they failing in the middle of the geometry optimization job, for example at Geom step 53 or 82?

 Hard to say, without knowing any details. Keep in mind, that also
conjugate gradient optimisation can lead to non-physical geometries, as
it does not optimize along the forces as steepest descent, or an MD with
simulating anealing would do. If you system is very unstable (with huge
forces), the best practice is too take steepest descent with a small
step size, until forces go down enough, so that you can safely use CG.

 Best regards

  Bálint

-- 
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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