[Wien] (no subject)

[delamora]

The simplest perivskite is
a=b=c
alpha=beta=gamma=90
A: 1/2,1/2,1/2
B: 0,0,0
O: 1/2,0,0
    0,1/2,0
    0,0,1/2
space group 221
so, if you have alpha=89.999 you can adjust to 90.
Now, if you have alpha=89.9 you can adjust to 90 for learning purposes, the calculation will be quite fast, but the final calculation you should use 89.9 and the pbnm group that has lower symmetry
    Pablo

________________________________________
De: wien-bounces at zeus.theochem.tuwien.ac.at <wien-bounces at zeus.theochem.tuwien.ac.at> en nombre de Víctor Luaña Cabal <victor at fluor.quimica.uniovi.es>
Enviado: jueves, 23 de abril de 2015 07:54 a. m.
Para: A Mailing list for WIEN2k users
Cc: Victor Luaña
Asunto: Re: [Wien] (no subject)

On Thu, Apr 23, 2015 at 05:56:00PM +0530, Shakeel Khandy wrote:
> I m a beginner and i want to study a compound of ABO3 type pervoskite with
> space group *pbnm*.I have got confused with the atomic positions of
> *pbnm *spacegroup.
> Although the experimental atomic positions are in my hand,but the problem
> lies in the negative atomic positions given by experimental data. Is there
> any other method to have the required atomic positions.

Shakeel,

1) The crystallographic description of coordinates assumes periodicity.
   So x=-0.12 is identical to 1+x=1-0.12. Any crystallographer is trained
   to do the operation quickly and the easy way is thinking

    1 = 0.999999999(10)
          --------- as mant 9's as it is needed

2) ¿Don't have a professor to traing you? ¿Don't have books on
   crystallography available?

3) Assuming the answers are NO in both cases let me recommend
   you some materials appropriate to the level of your question

a) My own slides on the subject

   <http://azufre.quimica.uniovi.es/DetEst/>

   Sorry by the spanish. Use google translate as you need.

b) An excellent and recent manual by italian crystallographers:

   C. Giacovazzo, Ed. Fundamentals of crystallography, IUCr & Oxford Univ Press
   IUCR: 0198555784, 1992

   There is a new edition, but I don't have it al hand.

4) This type of question should be solved by your prof./teacher

Good luck,
          Dr. Víctor Luaña
--
     .  .    DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
    / `' \   "I think the problem, to be quite honest with you,
   /(o)(o)\  is that you have never actually known what the question is."
  /`. \/ .'\
 /   '`'`   \ "Lo mediocre es peor que lo bueno, pero también es peor
 |  \'`'`/  | que lo malo, porque la mediocridad no es un grado, es una
 |  |'`'`|  | actitud"
  \/`'`'`'\/          -- Jorge Wasenberg, 2015
===(((==)))==================================+=========================
! Dr.Víctor Luaña, in silico chemist & prof. ! Mediocre is worse than
! Departamento de Química Física y Analítica ! good, but it is also
! Universidad de Oviedo, 33006-Oviedo, Spain ! worse than bad, because
! e-mail:   victor at fluor.quimica.uniovi.es   ! mediocrity is not a grade,
! phone: +34-985-103491  fax: +34-985-103125 ! it is an attitude
+--------------------------------------------+
 GroupPage : http://azufre.quimica.uniovi.es/
             (being reworked)
_______________________________________________
Wien mailing list
Wien at zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html