[DFTB-Plus-User] Format of the Slater-Koster files

[Roozbeh Anvari]

   Hi,

   I was wondering about how DFTB+ rotates H and S,  for example for a p-p
interaction : ( reference:: DFTB+%SK.F90%subroutine pp(hh, ll, mm, nn, sk)
) :
    "
    hh(1,1) = (1.0_dp-nn**2-ll**2)*sk(1)+(nn**2+ll**2)*sk(2)
    hh(2,1) = nn*mm*sk(1)-nn*mm*sk(2)
    hh(3,1) = ll*mm*sk(1)-ll*mm*sk(2)
    hh(2,2) = nn**2*sk(1)+(1.0_dp-nn**2)*sk(2)
    hh(3,2) = nn*ll*sk(1)-nn*ll*sk(2)
    hh(3,3) = ll**2*sk(1)+(1.0_dp-ll**2)*sk(2)
    "
   while, (Slater, J. C., & Koster, G. F. (1954) . *Physical Review*, *94*(6),
1498.) :
      Exx = ll**2 *(pp_sigma) - (1-ll**2) *(pp_pi)
      Exy = ll*mm *(pp_sigma) - ll*mm *(pp_pi)
      Exz = ll*nn *(pp_sigma) - ll*nn *(pp_pi)

here, could you please confirm the relative directions of the directional
cosines and also sampled energy integrals in the .SKf files ?  i.e. ( (ll ,
mm , nn) == (dx, dy , dz ) &  (hh(1,1) , hh(1,2),  hh(1,3) == (Ex,x,Ex,y
Ex,z)  ? )

2.
how accurate would be the calculated band structure without taking into
account the potential shift  in H = H0 + shift ?  the E-K I have calculated
using just H0/S from .SKF looks very similar to
    that given by dftb+ and dft, but band widths are significantly
narrower,

Best regards
Roozbeh






On Thu, Sep 19, 2019 at 2:02 PM Roozbeh Anvari <roozbeh.anvari at gmail.com>
wrote:

> Dear Balint,
>
> thank you for your help,
>
> Best regards,
> Roozbeh
>
>
>
>
> On Thu, Sep 19, 2019 at 5:08 AM Bálint Aradi <aradi at uni-bremen.de> wrote:
>
>> Dear Roozbeh,
>>
>> > I wonder why the overlap values are so large, are not the RAW values
>> > normalised ?
>>
>> The first few lines are only placeholders (historical heritage...).
>> Aftert that, the overlap integrals are less than one. For homonuclear
>> cases, identical orbitals (e.g. H-H  Sss0) give values close to 1 (makes
>> sense), while different orbitals or heteronuclear cases yield values one
>> order of magnitude lower.
>>
>> > To check this, I am searching where skHamCont and skOverCont  are read
>> > from  .SKF but have not found it yet,
>>
>> The reading of skf and construction of the containers happens in
>> multiple steps at multiple places:
>>
>>
>> https://github.com/dftbplus/dftbplus/blob/master/prog/dftb+/lib_type/oldskdata.F90
>>
>>
>> https://github.com/dftbplus/dftbplus/blob/1a31db05a60ad37ce9013b66dca4388a94b72817/prog/dftb%2B/lib_dftbplus/parser.F90#L2526
>>
>>
>> https://github.com/dftbplus/dftbplus/blob/master/prog/dftb+/lib_dftb/slakocont.F90
>>
>>
>> I hope this helps.
>>
>>   Best regards,
>>
>>   Bálint
>>
>>
>> --
>> Dr. Bálint Aradi
>> Bremen Center for Computational Materials Science, University of Bremen
>> http://www.bccms.uni-bremen.de/cms/people/b-aradi/
>>
>>
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>>
>
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