The ABINIT Users Mailing List ( CLOSED )

[Josef Zwanziger <jzwanzig@gmail.com>]

Dear Igor,

when I run v5/t37 all the way to the end (upping ntime from the value
2, which is used in the tests just to keep it short), it converges to
a BC tetragonal cell, like it should: here's the final cell geometry-

Unit cell characteristics :
acell=  8.4892915048E+00  8.4892915048E+00  8.4892915048E+00
rprim= -6.5662241853E-01  6.5662241853E-01  3.7107142032E-01
           6.5662241853E-01 -6.5662241853E-01  3.7107142032E-01
           6.5662241853E-01  6.5662241853E-01 -3.7107142032E-01
   ucvol=  3.9152838280E+02 Bohr^3
   lengths=  8.4892915048E+00  8.4892915048E+00  8.4892915048E+00 Bohr
   angles (23,13,12)=  97.91442980  97.91442980 136.43658054 degrees

this is done with the PAW dataset provided by the test suite. What
pseudopotential are you using, and cell geometry are you getting?

Joe


On Wed, Jul 15, 2009 at 6:54 AM, Igor
Lukacevic<ilukacevic@fizika.unios.hr> wrote:
> Dear abinit users,
>
> I am having some problems while trying to relax the body centered tetragonal
> phase of Si (beta-tin) using primitive unit cell with optcell=2.
>
> First I have tried with abinit-5.4.4p version, which stopped the calculation
> usually in the 1st or 2nd broyden step of dataset 2 (when cell size began to
> change), saying that the rprim change is too large, while I knew that it
> could not be. Whatever I put for dilatmx and starting aproximation of acell
> did not help. I did notice that when dataset 2 starts, it does not start 
> with
> the acell I gave it through the input file (a=b and c), but it changed the
> acell values to the ones corresponding to the cubic cell (a=b=c).
> How come that this happens?
>
> Then I saw that newer versions of abinit 5.7 and 5.8 have a bug fixed
> concerning the symmetry preservation during relaxation in body centered
> tetragonal cells when one uses optcell=2 (test v5, t37). Using 5.8.3 version
> indeed made the calculation continue and finish, but the final result is
> rather confusing. I always get a cubic cell in the end. This is the 
> analogous
> result to the one in t37.out from v5 test.
>
> I would like to know why this happens and how come that I do not get a 
> relaxed
> tetragonal unit cell in the end?
>
> The same things happen with a body centered orthorhombic unit cell of Si 
> Imma
> phase.
>
> Using nonprimitive unit cell does not have this problem (but the calculation
> is ofcourse longer).
>
> The calculations are tried on 3 different computers with versions 5.4.4p and
> 5.8.3.
>
> Input file is attached (the parameters are not at their converged values, 
> but
> I think that does not influence the issue).
>
>
> Thank you all in advance for your help!
>
> Yours Igor Lukacevic
>
> --
> Igor Lukacevic
> Department of Physics
> University of J. J. Strossmayer
> Trg Ljudevita Gaja 6
> 31000 Osijek
> Croatia
>



-- 
Josef W. Zwanziger
Professor of Chemistry
Canada Research Chair in NMR Studies of Materials
Director, Nuclear Magnetic Resonance Research Resource (NMR-3)
Dalhousie University
Halifax, NS B3H 4J3 Canada
tel: +1 (902) 494-1960
fax: +1 (902) 494-1867
web: http://jwz.chem.dal.ca
jzwanzig@gmail.com, jzwanzig@dal.ca