The ABINIT Users Mailing List ( CLOSED )

[Igor Lukacevic <ilukacevic@fizika.unios.hr>]

Dear Joseph,

The mailing list web interface seems to be down, so I'm also sending you the 
response directly (I'll also try to reply to forum).

You are apsolutely right. I have not payed attention to rprim values, only to 
acell ones. I appologize for doubting your results.

I get similarly

 Unit cell characteristics :
  acell=  6.5353079473E+00  6.5353079473E+00  6.5353079473E+00
  rprim= -6.5091379315E-01  6.5091379315E-01  3.9066925624E-01
          6.5091379315E-01 -6.5091379315E-01  3.9066925624E-01
          6.5091379315E-01  6.5091379315E-01 -3.9066925624E-01
  ucvol=  1.8480526756E+02 Bohr^3
  lengths=  6.5353079473E+00  6.5353079473E+00  6.5353079473E+00 Bohr
  angles (23,13,12)=  98.77893312  98.77893312 134.00770223 degrees

which gives tetragonal cell. The rprim values are not converged because of 
low 
ecut and ngkpt. But I have a question also: how does one now get the 
conventional unit cell parameters a=b and c? I looked at Burns&Glazer, but 
could not figure out. While considering without reference, it seems that one 
should do:

a = 2*acell1*rprim1
b = 2*acell2*rprim2
c = 2*acell3*rprim3

But I am not sure about this. Is this correct?

Thank you very much!

Igor

On Wednesday 15 July 2009 12:32, Josef Zwanziger 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

-- 
Igor Lukacevic
Department of Physics
University of J. J. Strossmayer
Trg Ljudevita Gaja 6
31000 Osijek
Croatia