[Pw_forum] Re: Pw_forum digest, Vol 1 #1325 - 4 msgs

[Malgorzata Wierzbowska]

On Mon, 29 Jan 2007, Srijan Kumar Saha wrote:


>  Respected Users,
>
>  Would you like to tell me what automatic  (like 48 48 1)
>  the dense k-point grid in the first scf calculations
>  (i.e. scf-fit). I should  use
>  to get  special q point
>> 
>> 0.6666667   0.0   0.0
>> as a  the subsets of the scf-fit ????
> Is there any definite rule except applying  a trial and
> error method like  4 4 1, 6 6 1, 9 9 1, 38 38 1 etc. etc.  ????
> Your kind help will be greatly appreciated.
> Regards,
> Amit
>

    If q=(2/3,0.0,0.0) your k-mesh for phonons and k-fit mesh
    should be modulo 3. So  (4 4 1) and (38 38 1) are for sure bad.
    Meshes (6 6 1) and (9 9 1) are too small, although they would
    not give the error if your rare k-mesh (k-mesh for phonons) were
    modulo 3.
    Actually, for this kind of calculations you should ask for
    3 meshes: k_fit, k_phonon, q_phonon.
    And always k_fit/(k_phonon + q_phonon) should be the integer
    number.

    Gosia



> On 1/29/07, Malgorzata Wierzbowska <wierzbom at ts.infn.it> wrote:
>> 
>> On Sun, 28 Jan 2007, Amit Kumar wrote:
>> 
>> 
>> > Respected Users,
>> >
>> > I'm getting following error  in new version of pwscf code to calculate
>> > electron phonon coupling.
>> >
>> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>> >    from elphsum : error #         1
>> >    q is not a vector in the dense grid
>> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>> >
>> 
>>     The above error and the question has been answered on pw-forum.
>>   The phonon grid q and the k-mesh for phonon calc. should be
>>   the subsets of the dense k-grid in the first scf calculations
>>   (i.e. scf-fit).
>> 
>>   Gosia
>> 
>> 
>> > when  I'm using only one special q point
>> >
>> > 0.6666667   0.0   0.0
>> >
>> > ( Can anyone  tell me is the above co-ordinates correct  for Graphite
>> > K-POINT???? )
>> >
>> > There is no error if I use the old version's scf nscf phonon nscf elec
>> > phonon method
>> > instead of using new version's la2F=.true. procedure with automatic
>> k-point.
>> >
>> > How to get rid of this error in the new version????
>> > Your kind help will be greatly appreciated.
>> >
>> > Regards
>> > Amit
>> >
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>