Use the optimised structure with the optimised unit cell. What else? SB 

> On 3 Jul 2021, at 11:01, Jibiao Li <[email protected]> wrote:
> 
> Dear All,
> 
> I have the same concerns about phonon calculations under pressures which was 
> posted on 
> Fri, 09 Dec 2016 23:33:04  
> <https://www.mail-archive.com/[email protected]&q=date:20161209>
> 
> To this end, vc-relax calculations with pressures are performed to get a 
> compressed geometry in the beginning. However, no keywords on external 
> pressures are required in input files of the subsequent phonon calculations. 
> In doing so, you actually can not differentiate an optimized structure at a 
> pressures and the unoptimized structure with the stresse. How do you know the 
> phonon calculations are truly targeting at a compressed structure at a 
> pressure. In my understanding, it is simply phonon calculations of an 
> unoptimized structure with stresses. It's definitely unstable. Shall we still 
> expect structural stability signatures from the phonon calculations of 
> optimized structures at pressures. How do we judge stability of a structure 
> at a pressure from phonon calculations? These questions puzzled me for a long 
> time. Could any body help me?
> 
> Best
> Dr. Jibiao Li,
> Department of Material Science and Engineering
> Yangtze Normal University
> Juxian Dadao 16#, Fuling, Chongqing, China
> Email: [email protected], [email protected], [email protected]
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— 
Stefano Baroni - Trieste —  http://stefano.baroni.me 
<http://stefano.baroni.me/> 




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