[Pw_forum] Small U for Co in ZnO for LDA+U (update)

[Nicola Marzari]

Dear Nektarios,


thanks for the update. Maybe Matteo Cococcioni or other could chip in -
could it be that the atomic orbital in the Co psp was not normalized,
so only when ortho-atomic or norm-atomic are applied the normalization
constant is taken into account ?

If the case, is it correct to say that norm-atomic and atomic are doing
the same thing, but norm-atomic automatically normalizes the projection
(something that should have been there in the Co psp to begin with) ?


Best,

					Nicola


Nektarios Lathiotakis wrote:
> Hi again,
> 
> As I wrote previously I have a Co impurity atom in ZnO and
> trying to find the right Hubbard-U for Co by fitting to experimental Co-d
> projected band  from J. Appl. Phys. 103 07D130 (2008). A typical input 
> file is in my
> previous e-mail.
> 
> I played with U_projection_type parameter and:
> 
> 1) 'ortho-atomic' and 'norm-atomic' agree and give the same optimal U for Co
> that is around 4eV. Very reasonable value and no referee would ever object.
> 
> 2) 'atomic' (the default) gives as optimal U 0.5eV which is much smaller.
> 
> In other words the Co-d projected band you get with 
> U_projection_type='ortho-atomic'
> and U_Co = 4 eV is the very close to the band you get with 
> U_projection_type='atomic'
> and U_Co = 0.5 eV.
> 
> Why is that difference? The problem with changing the U_projection_type 
> is that only
> atomic supports forces.
> 
> Thanks in advance and also to Nicola for his previous reply.
> Nektarios

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Prof Nicola Marzari   Department of Materials Science and Engineering
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