[Pw_forum] Phonon frequency: nat_todo option

[Vikan Manmathan]

Thank you Stefano.

I will try your suggestions.

*NANDHA KUMAR V.*
Research scholar,
IISER, PUNE.

On Sat, Oct 22, 2016 at 9:15 AM, stefano de gironcoli <degironc at sissa.it>
wrote:

> Dear Vikan,
> I dont have direct experience on this problem. here a few things i would
> look into:
>
> from your NEB calculation around the TS you should be able to see what the
> unstable mode is expected to look like and how many atoms are involved.
> If you compute interatomic force constants (IFC) only around a subset of
> the atoms there is the problem of how you impose the acoustic sum rule.
> One way would be to complete your DynMat using the IFC of the bulk
> material (that you could compute separately), and impose ASR on this model.
> To stay on the safe side you could set the mass of the atoms that you did
> not compute to a very large number so they do not move.
>
> stefano
>
>
>
> On 21/10/2016 17:38, Vikan Manmathan wrote:
>
> Dear Developers and Experts,
>
> I am interested in studying diffusion of metal clusters on oxide support.
> As a first step, I took a simplest case (adatom hopping) and obtained the
> transition state using CI-NEB method.  I want to find the rate constant for
> the above, I need to know the normal mode vibrational frequencies at
> initial and transition states.
>
> So I calculated the phonon frequencies using frozen atomic coordinate (nat
> _todo option only on metal adatom) since the system size is very large.
> I expected the transition state to have one less real frequencies (3N-1)
> relative to initial state (3N). However, I am getting 3N real frequencies
> for the transition state (correct me if I am wrong).
>
>  I have also checked it by including more atoms in the linear response (up
> to 33 atoms) but still I got 3N real frequencies for the TS.
>
> I have attached the input files and the output file generated by dynmat.x
>
> Any suggestion will be highly appreciated.
>
> Thanks in advance.
>
> regards,
>
> *NANDHA KUMAR V.*
> Research scholar,
> IISER, PUNE.
>
>
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