[Pw_forum] Stress tensor from pw.x and cp.x

[Lawrence Lee]

Dear all,

Since my calculation is really simple, I am not going to attach my input
file here. I use the QE-3.1.1 code, and perform scf calculation using
pw.x on a 64-atom cell, which has a perfect fcc structure, using only
the gamma point. I obtain a stress tensor then.

Later on I use exactly the same structure and cell and cut-off's, but
using cp.x to perform a damped dynamics on the electrons, keeping the
atoms fixed. I also obtain a stress tensor.

However, the results between pw.x and cp.x is different, apart from the
difference in units. The cp.x results are generally about 5~10 GPa above
that of pw.x.

I find this quite confusing. Is the method of calculation of stress
tensor by these two programmes different?

Thank you very much for solving my doubt.


-- 
S.H. Lee
M.Phil
Physics Division
The CUHK Graduate School

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