[QE-users] mechanical stability under pressure from phonons

[Uri Argaman]

Hi all
In the literature the mechanical stability condition using elastic
constants includes explicitly the pressure:
In cubic symmetry, for example:
C11 + 2*C12 +P>0;
C44 +P>0;
C11 + C12 + 2*P>0;
from: Grimvall et al. REVIEWS OF MODERN PHYSICS, VOLUME 84,  2012
In this paper, they write: " There seems to be no rigorous discussion of
this point in papers that have presented ab initio calculations of phonon
dispersion curves under pressure,..."
The stability condition from phonons: omega>0 for all modes. It seems that
it is not equivalent, because the phonon condition is at constant volume.
Is it known what is the condition at constant pressure?
Than you very much
Uri Argaman
Ben-Gurion University of the Negev
Israel
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