[Pw_forum] A soft phonon at Gamma point

[Stefano Baroni]

Hi Lijun Zhang. I would say it is a phonon instability (like the one  
occurring in ferroelectricity). An elastic instability would be  
signaled by a sound velocity going to zero. SB

On Feb 5, 2006, at 11:53 AM, Lijun Zhang wrote:

> Dear all,
> I am doing some calculations on pressure-induced phase transitions.
> With increasing pressures, It is found that a mode softens exactly  
> at Gamma
> point.(higher pressure, more negative value) Does it represent a  
> phonon instability or an elastic instability?
> Thank you in advance.
>
> Lijun Zhang
>
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
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