[Wien] Reg: BerryPI calculation

[Sheikh Jamil Ahmed]

You can create non equivalent atoms using the w2web interface.  You have to
use the "split" options to divide the two equivalent positions of Atom 1
into two different atoms. And then label them as 1 and 2 which will make
sure that the symmetry operation doesn't realize that you have two
equivalent positions. Then you can go on to compute the effective charge
for atom 1.

Alternatively, on your current structure both the atoms are equivalent
which means they will have the same effective charge. So, I would suggest
that instead of displacing just one atomic positions if you use identical
displacement for the both positions, you can compute sum of the effective
charges for the two equivalent atoms without any errors. Then you just have
to average them.

PS: make sure that you lattice vectors are orthogonal. BerryPI doesn't yet
have the capability to compute polarization for non orthogonal case.

Hope that will help.

Sheikh


On Sun, Oct 13, 2013 at 5:26 AM, Shwetha Gummula
<shwetha.gummula at gmail.com>wrote:

> Dear Wien2k users and developers,
>            I want to calculate the Born effective charges by using the
> BerryPI code which is in interface with the wien2k. I have successfully
> installed and ran the examples. In order to calculate the Born effective
> charges of particular atom in particular direction we have the change the
> position of that particular element in the particular direction.  But my
> question is for my compound which is tetragonal structure (ABO4 type), for
> particular atom A it created equivalent atoms.
> Ex:ATOM  -1: X=0.00000000 Y=0.75000000 Z=0.37500000
>           MULT= 2          ISPLIT=-2
>       -1: X=0.00000000 Y=0.25000000 Z=0.62500000
> A         NPT=  781  R0=0.00000500 RMT=    2.1200   Z:
>  if i change the position of one atom while initializing it is giving
> error about the other equivalent position where there position also have to
> change.
> Ex:ATOM  -1: X=0.00000000 Y=0.75000000 Z=0.36500000
>           MULT= 2          ISPLIT=-2
>       -1: X=0.00000000 Y=0.25000000 Z=0.62500000
> A         NPT=  781  R0=0.00000500 RMT=    2.1200   Z:
>
> In order to change the position (or perturb) do i have to create the again
> in w2web page with the perturbed positions (A (0 0.75, 0.365)). What will
> be the correct procedure. How to create the non equivalent positions for
> every element so that we can easily perturb the positions. please can
> anyone help me regarding this.
> Thanking you
>
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