[QE-users] Pressure difference from the vc-relax and SCF

[Mofrad, Amir Mehdi (MU-Student)]

Hi everyone,

I have a few questions (please see below). I apologize if this post is repetitive. The previous posts/tutorial slides on the internet didn’t address these.

The value for pressure at the end of vc-relax converges to zero, but right after that, in the SCF cycle it gives a different value. Doesn't it do the SCF cycle on the converged structure? If yes, then why is the pressure different? I think I read somewhere that one uses a fixed number of plane waves, whereas, the other one uses a fixed Ecut. Do you know why this is?

What is the physical meaning of this pressure (being negative or positive) from an scf calculation on an optimized structure from vc-relax output?

Thank you in advance for any help or ideas you have.



Best,


Amir M. Mofrad

Graduate Research Assistant

Graduate Teaching Assistant

Chemical Engineering Department

University of Missouri
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