[DFTB-Plus-User] (no subject)

[Ben Hourahine]

Hello Hegoi,

which version are you using, the DFTB+ Snapshot 081217 or 1.0.1 ?
If you aren't using 081217, try that first.

I don't know the history of your Ca parameters, or your geometry,
so can't advise further, as there are many things that could in
principle cause this (non-relaxed initial geometry containing a
lot of potential energy for example).

Cheers

Ben

hmanzano at labein.es wrote:
> Hello DFTB+ users
> 
> I am trying to run a MD simulation on a system containing Ca-Si-O-H.
> After a correct behaviour one the first 50 steps, the SCC convergency
> fails, and I get other 50 steps later the same error reported in this
> message:
> 
>>Dear Haydee Valdes,
>>
>>> I would like to run an MD calculation using DFTB+.
>>> I am starting from an DFTB+ optimized geom  but I get the following
> message
>>>
>>> ERROR!
>>> -> Failure in diagonalisation routine dsygvd, non-positive definite
> overlap! Minor  866 responsible.
>>>
>>
>> Without the concrete example, I can't really any specific advise.
>>However, the failure message as above is ususally cause by "ill"
>>geometries, for example two atoms on the top of each other in a periodic
>>structure.
>>
>> Regards
>>
>>    Bálint
> 
> Analysing my results, I show that, as Dr. Aradi said, the error appears
> when an H atom gets to close to an O, they collapse. I have tried with
> 0.1 fs time steps, small enough I think, and also a Non-SCC calculation.
> I have red that in the current version there is a strange behaviour of
> the H atoms during MD. Is this case? Is there any way to overcome the
> problem?
> 
> Thank you
> 
>              Hegoi
> ____________________________
> Hegoi Manzano
> 
> e-mail:  hmanzano at labein.es <mailto:hmanzano at labein.es>  
> Tel:   94 607 3300  ext. 2774
> Fax: +34-946073349
> 
> Nanomaterials on construction , NANOC.
> LABEIN-TECNALIA
> C/ Geldo, edif 700
> Parque Tecnológico de Bizkaia
> 48160 Derio, Bizkaia
> 

-- 
     Dr. B. Hourahine, SUPA, Department of Physics,
   University of Strathclyde, John Anderson Building,
          107 Rottenrow, Glasgow G4 0NG, UK.
    +44 141 548 2325, benjamin.hourahine at strath.ac.uk
   The University of Strathclyde is a charitable body,
registered in Scotland, with registration number SC015263