[Pw_forum] Phonon_quarry

[Stefano Baroni]

To be more precise: it does not make any sense to "displace" any atom by any specific amount. Forces on any other atoms will be linear in the amplitude of the displacement by construction (they are calculated in the linear-response regime), and energy difference quadratic therein. It can make sense to ask what it is the force linear responce to the displacement of any specific atom in any specific direction, though: this is obtained by calculating the interatomic force constants, by using a procedure that you certainly know. If you don't, it may be worthwhile to take a glance at how this is done, starting from google, or, even better, from some good old fashioned bibliographic search ... SB

On May 7, 2010, at 7:07 PM, Paolo Giannozzi wrote:

> partha sarathi ghosh wrote:
> 
>> How to calculate phonon dispersion curve using ph.x that I know
>> but I want to displace a particular atom in a particular direction
>> with adjustable displacement.
> 
> doesn't make sense to me. There is no "real" dispacement in the
> phonon code (unlike in "frozen phonon" method): the linear response
> to a displacement is calculated instead
> 
> P.
> -- 
> Paolo Giannozzi, Democritos and University of Udine, Italy
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
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