[Pw_forum] k points in epsilon.x

[marsamos at democritos.it]

Dear User, for generating a kpoint grid supported by epsilon you can 
use the following small program (for pwscf input you have to specify 
nosym=.true., and KPOINTS crystal)

program kpoints_gen

integer :: ikz, iky, ikx, nk
real :: weight
real :: shiftx, shifty, shiftz

read(*,*) nkx, nky, nkz, shiftx, shifty, shiftz

nk=nkx*nky*nkz
weight=1.0/real(nk)
write(*,*) nk
do ikz=1,nkz
do iky=1,nky
do ikx=1,nkx

write(*,"(4f15.9)") (real(ikx)-real(1.0)+shiftx)/real(nkx), 
(real(iky)-real(1.0)+shifty)/real(nky), &
           (real(ikz)-real(1.0)+shiftz)/real(nkz), weight

enddo
enddo
enddo


end program kpoints_gen


BUT I strongly suggest to you to use or the utilities inside SaX (see 
www.sax-project.org) or yambo (www.yambo-code.org) for calculating the 
dielectric constant. epsilon.x is not complete (it does not include the 
nonlocal part of the pseudo potential and is not able to include in the 
calculation the non-local field effects and excitonic effects). If YOU 
WORK WITH SEMICONDUCTORS OR INSULATORS YOU WILL NOT BE ABLE TO COMPARE 
WITH EXPERIMENTS. You should now which kind of RESPONSE you want to 
reproduce.

bests

layla



Quoting Gabriele Sclauzero <sclauzer at sissa.it>:

>
>
> dev sharma wrote:
>> Sir, i want to calculate dielectric constant as a function of
>> frequency.  I have read the manual And it is written there that
>> Epsilon.x doesn't support the reduction of the k-points grid into the
>> unreducible Brillouin zone, so the previous PW runs must be performed
>> with a uniform k-points grid and all k-points weights must be equal to
>> each other, i.e. in the k-points card the k-points coordinates must be
>> given manually in \emph{crystal} or \emph{alat} or \emph{bohr}, but not
>> with the \emph{automatic} option.
>
> In your first mail you were speaking about the automatic keyword as 
> if it was an option
> for a k-point list to be supplied to epsilon.x. As you have now 
> reported from the manual,
> epsilon.x does not need a k-point grid, since it uses the k-points 
> from the underlying
> data produced by the previous pw.x run.
> For a cubic symmetry system, for instance, you can supply manually a 
> N x N x N mesh of
> k-points (using crystal option might be the easiest solution, in my 
> opinion), which must
> provide a good sampling the full BZ (it is not difficult to produce 
> one, see the source
> code of pwtools/kpoints.f or PW/kpoint_grid.f90).
> Be careful and check the code does not reduce the mesh by symmetry 
> (which is the default,
> good behaviour of the code, that in this specific case you want to 
> avoid). Use the nosym
> option if needed (as written in the manual).
> You can also try to generate the grid with the automatic option of 
> K_POINTS after setting
> to true nosym and noinv (see Doc/INPUT_PW.txt), but I'm not sure if 
> this always works.
>
>
> Regards,
>
> GS
>
>
>
>> Thanks
>>
>> On Mon, Oct 12, 2009 at 12:40 PM, Gabriele Sclauzero <sclauzer at sissa.it
>> <mailto:sclauzer at sissa.it>> wrote:
>>
>>
>>     dev sharma wrote:
>>      > hi 2 all,
>>      >
>>      >  I have one question. In epsilon.x, the k points is not automatic
>>      > option. Sir, means how to give the K points option i.e. we have
>>     to give
>>      > only irreducible k points or like for the calculation ='bands' ,
>>     we have
>>      > give the path (like G{0,0,0}-->X(0.5,0,0)). If we have to give the
>>      > irreducible points , how to calculate those points ???? can i do
>>     this ,
>>      > that run the pw.x with a mesh like 4*4*4 grid  and the number of k
>>      > points in the scf output are the required k points
>>
>>     Never used this utility, so maybe my advice is useless: are you sure
>>     that epsilon.x does
>>     need a k-point grid on input? For what purpose are you using the
>>     program? Do you know what
>>     it computes? If not, please look at the documentation in
>>     Doc/eps_max.tex.
>>
>>
>>     GS
>>
>>
>>     PS: Please always sign your mails with your name and affiliation. Thanks
>>
>>
>>
>>     --
>>
>>
>>     o ------------------------------------------------ o
>>     | Gabriele Sclauzero, PhD Student                  |
>>     | c/o:   SISSA & CNR-INFM Democritos,              |
>>     |        via Beirut 2-4, 34014 Trieste (Italy)     |
>>     | email: sclauzer at sissa.it <mailto:sclauzer at sissa.it>
>>               |
>>     | phone: +39 040 3787 511                          |
>>     | skype: gurlonotturno                             |
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> --
>
>
> o ------------------------------------------------ o
> | Gabriele Sclauzero, PhD Student                  |
> | c/o:   SISSA & CNR-INFM Democritos,              |
> |        via Beirut 2-4, 34014 Trieste (Italy)     |
> | email: sclauzer at sissa.it                         |
> | phone: +39 040 3787 511                          |
> | skype: gurlonotturno                             |
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