[QE-users] Doubts on phonon calculations under pressures

[Jibiao Li]

Dear All,

I have the same concerns about phonon calculations under pressures which was posted on  Fri, 09 Dec 2016 23:33:04 

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: jibiaoli at yznu.edu.cn, jibiaoli at foxmail.com, jibiao.li at hotmail.com
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