[QE-users] Problem obtaining reliable cell constants from vc-relax (molecular crystals)

[Christoph Wolf]

Hi Eric,

your structure is quite complex so the less than perfect agreement can have
several causes.

first I would check if the calculation is converged with respect to cutoff
and k-points. In particular forces require higher cutoffs than energy
convergence (~20%) in my experience.
Are your pseudos ultrasoft/PAW? Otherwise ecutrho=4*ecutwfc should be
sufficient. Grimme-D3 is now available in QE as well.

Generally the agreement is not too bad; it depends what you are attempting
to calculate next!

Best,
Chris

-- 
Postdoctoral Researcher
Center for Quantum Nanoscience, Institute for Basic Science
Ewha Womans University, Seoul, South Korea
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