Dear Apu,
all this is a questions of the choice of origin. Looking in Int. Tables
one sees the conventionally a site with -3m. symmetry is taken as
origin (octahedral site of hcp), and not the 1/3 2/3 1/4 site, which
has -6m2 symmetry, and therefore no inversion centre.
The problem is that in many textbooks the sites given by you are listed
for the metal atoms and figures are drawn accordingly. This does,
however, not comply with the conventions concerning choice of origin
for space groups, where sites with centre of inversion are preferred,
except if there is a site with smaller frequency (thus higher point
group symmetry). In that case the latter choice is also employed and
two settings are given (setting 1 with highest point group symmetry and
setting 2 with centre of inversion): best known example: Fd-3m.
According to my knowledge GSAS works like most programmes with the
conventional setting from Intern. Tables, and if there are two
settings, with setting two including centre of inversion at the origin.
Best regards
Andreas
[EMAIL PROTECTED] wrote:
Dear (Sir) Stefano Agrestini,
Thank you for your help. Now I am getting good result, but I am
confused also. I will be grateful to you tell me how do you determine
the atom coordinate as (1/3, 2/3, 1/4) in case of Zirconium (p 63/m m
c), whereas the position of the atoms are (0,0,0) and (2/3, 1/3, 1/2).
What is the general rule for supplying the atoms coordinate in
GSAS? Is there any literature(help) on this topic?
Thanking you.
With best regards,
Apu
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Apu Sarkar
Research Fellow
Variable Energy Cyclotron Centre
Kolkata 700 064
phone: 91-33-2337-1230 (extn. 3190)
Fax: 91-33-2334-6871
INDIA
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----- Original Message ----- From: "Stefano Agrestini
(Bianconi)" <[EMAIL PROTECTED]> Date:
Saturday, October 2, 2004 11:05 pm Subject: Re: GSAS - p 63/m m
c > Dear Apu
> The correct information are:
> **Zr**
> Zirconium Metal hexagonal (Mg-type)
> 10.00 .010 1 .500
> 3.2320 3.2320 5.1470 90.0000 90.0000 120.0000
> P 63/M M C 194
> ZR 2c .3333 .6667 .2500 1.000
>
>
> Therefore you must give to GSAS only the 1/3 2/3 1/4 position. All
the
> other equivalent positions will be created automatically by GSAS
> throughthe space group P 63/m m c.
>
> Stefano Agrestini
>
> On Sat, 2 Oct 2004 [EMAIL PROTECTED] wrote:
>
> >
> >
> > Dear All,
> >
> > I am trying to do Rietveld refinement of Zirconium using
GSAS.
> Its space
> > group is p 63/mmc (194). It is a hexagonal closed packed
system
> with two
> > atoms per unit cell. Position of the one atom is (0, 0, 0)
and
> that of
> > the other is (2/3, 1/3, 1/2).
> <>
> > I am also giving the atom coordinates i.e. x,y,z as (0, 0, 0)
> for Zr1 and
> > (0.666, 0.333, 0.5) for ZR2 in GSAS.
> >
> > I think I am doing wrong because it is giving very bad
result..
> >
> > Please suggest what should I give as the atom coordinates.
> >
> > Thanking you all.
> >
> > Regards,
> >
> > Apu
> >
> > /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
> > Apu Sarkar
> > Research Fellow
> > Variable Energy Cyclotron Centre
> > Kolkata 700 064
> > phone: 91-33-2337-1230 (extn. 3190)
> > Fax: 91-33-2334-6871
> > INDIA
> > /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
> >
> >
> >
> >
>
>
>
>
--
Dr. Andreas Leineweber
Max-Planck-Institut fuer Metallforschung
Heisenbergstrasse 3
70569 Stuttgart
Germany
Telephone: +49 (0)711 689 3365
Telefax: +49 (0)711 689 3312
[EMAIL PROTECTED]
http://www.mf.mpg.de/de/abteilungen/mittemeijer/english/index_english.htm
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