[Wien] a question regarding space group and primitive cell

[shamik chakrabarti]

Dear Stefaan Cottenier Sir,

                                       Thank you very much for your reply.
It resolves all of our doubts.

with best regards,

Shamik Chakrabarti

On Fri, Dec 10, 2010 at 3:43 PM, Stefaan Cottenier <
Stefaan.Cottenier at ugent.be> wrote:

>
>                                We have done a calculation for a material
>> having space group *Pnma.* The material has *4 in equivalent* atoms and
>> total *20 atoms/unit cell*. Now if we use all the 20 atomic coordinates
>> of previous calculation and make *all of them inequivalent by changing
>> the space group to Primitive* then whether the calculation will give the
>> same results as earlier calculation??.....I am asking this question
>> because the structure (in Xcrysden) seems to be different.........
>>
>
> A static calculation (one scf-cycle) must give you the same result, yes. It
> will only take more time, because one can profit less from symmetry.
>
> If you allow geometry optimization, the final geometry might be different,
> however: perhaps an atom that is not longer constrained by symmetry might
> want to move to a different place.
>
> In order to convince yourself whether or not both structures are identical,
> it is much cheaper to inspect the neighbours rather than performing an scf
> cycle. Do 'x nn' for both structures, and compare the distances in
> case.outputnn.
>
> Stefaan
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>



-- 
Shamik Chakrabarti
Research Scholar
Dept. of Physics & Meteorology
Material Processing & Solid State Ionics Lab
IIT Kharagpur
Kharagpur 721302
INDIA
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