[Wien] Why is the calculated lattice volume only the half of the unit cell volume of CoSb3?

[Z.J.]

Well-beloved professor Stefaan,
    Thank you for your reply. Your reply is very helpful for me to
understand the essence.


2006/6/14, Stefaan Cottenier <Stefaan.Cottenier at fys.kuleuven.be>:
>
>
> >      I use the latest vision of wien2k to optimize the lattice
> > paremeter of CoSb3(space group is Im-3 and the number of space group
> > is 204). And I choose the option of "vary VOLUME with constant a:b:c
> > ratio" at the first step. The lattice parameter of CoSb3 is
> > 17.07955404 a.u. and the vomume of the unit cell is 4982.296631 cube
> > a.u.. There is no error in the process of calculation of optimization.
> > However, the calculated volume of unit cell is only the half of the
> > unit cell  volume of CoSb3.  Is the calculated result right? What is
> > the matter?Please help me. By the way, what is the relation between
> > the conventional cell and the unit cell of CoSb3? Thank you very much.
>
> In body centred symmetry (all space groups starting with I, or in wien2k
> convention with lattice type B in case.struct), the primitive unit cell
> has half the volume of the conventional unit cell. The lattice constants
> in case.struct are for the conventional unit cell. The :VOL label in
> case.scf is for the primitive one.
>
> Stefaan
>
>
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-- 
School of Materials Science and Engineering
Central South University
Z.J. Pan
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