[DFTB-Plus-User] Vibrational frequency calculation on DFTB+, how is it?

[Bálint Aradi]

On 02/11/2013 05:41 PM, Sol Milena Mejia wrote:
> Dear DFTB Plus Users
> 
> I am a new user of the DFTB+ capabilities.
> 
> I would like to venture into vibrational frequency calculations.
> 
> Therefore, I need to calculate the second derivates of the energy and obtain the 
> Hessian.out file in order to use the script available in the web page to run 
> frequencies calculations.  I understand from the manual that this is possible 
> with the next keyword: Driver = SecondDerivates, but I have doubts about the 
> Atoms Index and Delta Step size options

If your system is not too big (only a few hundred atoms), just use
SecondDerivatives without any options. Otherwise, you would have the
possibility to restrict the vibration calculations only to a subgroup of
your atoms (however, that is then somewhat unaccurate). As for the step
size: there is usually no need for adjusting it.

  Best regards,

  Bálint

-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b_aradi/


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