[Pw_forum] input for resp_mat.x in to optimize the U for LDA+U calculations

[matteo at umn.edu]

Dear Pieremanuele,

if you don't have the crystal coordinates of the atoms you can have the 
code print them.


On May 27 2009, Pieremanuele Canepa wrote:

>Dear all,
>I was  able to compile  the program resp_mat.f90 in order to  carry out the
>U in a self consistent way. Now I am trying to write up correctly the input
>for resp_mat.x. I have realized reading trough the guide (found at link
>http://vlab.msi.umn.edu/events/lecture.shtml)  that I do need to have an
>external file   with the fractional coordinate of the atom belonging to the
>supercell.
>Actually, if I look at those external file (call for example pos....) that
>come togheter with the guide found online, the second part is concerning to
>the fractional coordinate of the atoms in the supercell, while what is the
> first part? Are these the vector of the supercell in Cartesian 
> coordinates ?

yes.

>Why, when  for instance  the   Cartesian coordinate of the  supercell
>vectors printed in the early part of the PWscf output are:
>  crystal axes: (cart. coord. in units of a_0)
>               a(1) = (  1.000000  0.000000  0.000000 )
>               a(2) = (  0.000000  1.000000  0.000000 )
>               a(3) = (  0.000000  0.000000  1.000000 )
>in the file pos  these become
>20.d0 0.d0 0.d0
>0.d0 20.d0 0.d0
>0.d0 0.d0 20.d0
>?

it doesn't matter the length of the vectors. only the ratio between length 
does.
This is used to compute the distance between atoms ut the scale doesn't 
matter at all.


>The cell parameter  in this case is 10.8400 (FeNi in the guide)
>
>Another question is : what does the line   back = 'neutral' mean  in the
>input file for resp_mat.x?
>

neutral means that you are enforcing the total response of the system to be 
neutral. so there will be a compensating "background" term in the response 
matrix that results in an additional column and row. see PRB 71 35105.

hope this helps. 

regards,

Matteo


I hope  you can get my point!
>Best Regards, Piero
>