Dear Tomas,
at the moment I do not see something being obviously suspicious. Maybe
the culprit is some structural phase transition invalidating the
experimental structure you compare with. You might get one or two ideas
from Stefaan Cottenier's work?
Error Estimates for Solid-State Density-Functional
Theory Predictions: An Overview by Means of the
Ground-State Elemental Crystals
K. Lejaeghere , V. Van Speybroeck , G. Van Oost & S. Cottenier
http://dx.doi.org/10.1080/10408436.2013.772503
Best regards,
Martin
---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564
Am 10.11.2015 13:05, schrieb Tomas Kana:
Dear Martin and Gerhard,
Thank you for your suggestions. Gerhard, thank you for mentioning this
experimental work. Will you please send me the pdf
of the article? I do not have access to it.
Regarding Martin's questions:
I tried to include magnetism
of the constituents by performing spin polarized calculations, too,
but the equilbrium volume was the same. The forces within the
hexagonal unit cell
were not given in case.scf (I think there was too much symmetry
operations).
However, I recently tried to express the hexagonal unit cell in a
orthorhombic base
and cancel the symmetry operations by using inequivalent atoms
(I send the structure file in attachment). The volume was still wrong
but
I know the values of the forces. For the experimental
atomic volume they were at most 0.84 mRy/a.u.
With best regards
Tomas Kana
Since you ask for ideas and without really looking at the problem:
Assuming that the experimental numbers are correct, is this a room
temperature structure? The calculations are, of course, ground state
zero Kelvin, so things might go south if there is a phase transition
somewhere. Considering the elements you deal with maybe magnetic?
What
are the forces in your calculations?
Good luck,
Martin
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