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[matthieu verstraete <matthieu.jean.verstraete@gmail.com>]

You shouldn't be fixing the atoms for the first dataset: it probably
does nothing as is. Further, given the high symmetry of the xred, it
probably won't move the atoms anyway (if it should you might try less
symmetric positions: this might be keeping abinit from finding the bct
phase).

I notice you are looking for a high-pressure phase. Is the 12.5GPa
from experiment? It could be that your system is not even metastable
wrt cubic Si at that pressure (in DFT) and that you need a higher
pressure.

If you start from a non-cubic cell, and abinit makes it cubic, that
should be the right result (for your pseudos kpoints etc... of
course): it will not impose more symmetry, but should enforce the
initial one. What if you re-enter your final geometry into a new
input, does abinit find a different space group?

your tsmear is quite large, but with cold smearing this should be ok.
I would go down to 0.02 at most.

Matthieu

On Wed, Jul 15, 2009 at 12:32 PM, Josef Zwanziger<jzwanzig@gmail.com> wrote:
> 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
>



-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF)
Dpto. Fisica de Materiales,
U. del Pais Vasco,
Centro Joxe Mari Korta, Av. de Tolosa, 72,   Phone: +34-943018393
E-20018 Donostia-San Sebastian, Spain        Fax  : +34-943018390

Mail : matthieu.jean.verstraete@gmail.com
http://www-users.york.ac.uk/~mjv500