[DFTB-Plus-User] Failure in diagonalisation routine with atoms not too close

[Ben Hourahine]

Hello Mathias,

implementations of dsygvd are often unreliable. Try the alternative eigensolvers and see if that works:

Eigensolver = RelativelyRobust{}

this should be about the same performance but less likely to fail. The qr solver used by standard{} is slower but also should be more reliable.

Regards

Ben



On 19/01/16 12:43, Mathias Jørgensen wrote:
> Dear DFTB+ community
>
> I have been using the DFTB+ for optimising Mo2C clusters (Mo12C6) without problems. I use it for optimising initial random structures for a genetic algorithm (with atoms positioned randomly within a cell with some minimum interatomic distance). 
>
> Recently I moved to a larger system, MoC24H18, and I very often get the following error:
>
> "Failure in diagonalisation routine dsygvd, non-positive definite overlap! Minor 7688 responsible."
>
> where “7688” differs depending on the initial structure.
>
> For smaller systems the error still occurs but is much less frequent. 
> I learned from older posts on this error that the problem often has to do with atoms getting too close or other non-physical systems. In my case, however, atoms getting too close it not the problem - I checked a lot of the geometries and ran tests with large initial minimum interatomic distances. Also, I learned that 7688 refers to orbital 7688, but I certainly don’t have 7688 orbitals in my system, Mo(d)C(p)H(s). The error is consistent with respect to initial atomic configuration and it happens at geometry step 0.
>
> What could be wrong?
>
> Best,
> Mathias
>
> *********
> Mathias Jørgensen
> Phd. Stud.
> Interdisciplinary Nanoscience Center (iNANO), research group of prof. Bjørk Hammer
> Aarhus University
> Denmark
> email: mj at inano.au.dk
>
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