[DFTB-Plus-User] Failure of routine zhegvd

Bálint Aradi balint.aradi at bccms.uni-bremen.de
Wed Dec 10 08:42:53 CET 2008

Dear Hannah,

> I have just started using DFTB+, and am getting the following error a lot:
> -> Failure in diagonalisation routine zhegvd, non-positive definite overlap!
> Minor  ...  responsible.
> I understand that this can be caused by atoms too close to each other. But in
> one simulation I compressed my unit cell by only a small amount from
> equilibrium and received the error. Is this normal or is there sometimes
> another reason behind the error?

  No, it is not normal, except the geometry is strange in someway, or
you're are using a parameter set for something it is not meant to be
used for. Without a complete input it's difficult to judge, what the
problem really is.

> I also have gotten the error when I do nothing except change the kpoints.
> At the moment I'm simulating a unit cell of titanium dioxide.

  Just a question. You do not use the trans3d set for calculating TiO2
bulk, do you? Because that set is meant to be used for transition
elements in biological molecules (see the description on the webpage and
the referred papers). It was never aimed to working for bulk systems.
We're at the moment in the process in creating a TiO2 bulk set with
organics, but that's still work in progress.

  Best regards,


Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen

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