[Pw_forum] Primitive unitcell

[Stefano de Gironcoli]

The primitive unit cell is the one that contain the minimum number of atoms
so it is more computationally convenient from the computational point of 
view.
you can use the conventional one but it will contain more atoms.

the definition of the cell is described in the INPUT_PW.html file when 
discussing
ibrav and celldm variables.

...

ok but the P in Pnma(62) means primitive... isn't it ?

stefano


On 10/30/2012 11:26 PM, David Furman wrote:
> Dear users,
>
>   
>
> I was reading the tutorial "From Wyckoff to Quantum Espresso" (can be found
> in google) to make sure how to correctly
>
> write crystal input data. All examples seem to be using the primitive unit
> cell atomic positions (rather than the conventional unit cell). Is this
> actually so?
>
>   
>
> My question is how can I know the primitive unit cell atomic positions ?
>
>   
>
> I only have conventional unit cell coordinates and 3 cell parameters for a
> Pnma (62) crystal.
>
> Also, if I use the primitive unit cell coordinates, what value should I put
> to celldm(1)-celldm(3) ? is it the original conventional cell one ?
>
>   
>
> Many thanks,
>
> David Furman
>
>   
>
>
>
>
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