Your question is based upon a common misunderstanding of minimizing
forces. You are thinking that the time to optimize depends upon the
number of positions (3*Number of Pt atoms that move) which is wrong.
With PORT it scales as the number of clusters of phonon frequencies and
weakly with the width of the clusters; with MSR1a it scales as the
number of clusters of eigenvalues of the joint electron-phonon problem
and their width.

You will gain far more by generating a proper symmetric model with P-3m1
(maybe P-31m) symmetry rather than what you appear to have, a P1
structure. This will reduce the number of uniques phonon etc modes by
something like 6-12, and will be much faster and converge better.

Dear Laurence Marks,

When having created the most symmetric slab model that is relevant for the case at hand, wouldn't you agree that it still makes sense to fix the positions of the middle few layers to their bulk positions? One cannot make slabs as thick as to find spontaneously bulk behaviour in the center, and therefore imposing the bulk geometry in the slab center could be preferred over getting unphysical lattice spacings. Can you comment?

Thanks,
Stefaan


--
Stefaan Cottenier
Center for Molecular Modeling (CMM) &
Department of Materials Science and Engineering (DMSE)
Ghent University
Tech Lane Ghent Science Park – Campus A
building 903
BE-9052 Zwijnaarde
Belgium

http://molmod.ugent.be
http://www.ugent.be/ea/dmse/en
email: stefaan.cotten...@ugent.be

my conference talks on Youtube: http://goo.gl/P2b1Hs
for China: http://i.youku.com/cottenierlectures
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