[DFTB-Plus-User] Dear DFTB plus users. I am trying to construct the SK parameter file by myself. But i can understand some part.

[Bálint Aradi]

Dear Peter,

> 1.  Line 1  gridDist nGrdPoints
>      What is the unit for gridDist?  Is it angstrom or atomic unit?

Everything always atomic units (Bohr radius) unless explicitely declared
being something else.

> 
> 2. Line 4~4+nGridpoints-1:
>     The document mentions that in  this block , the distance will be
> increased one "gridDist" unit between each line. I would like to ask is
> the distance for line4 refering to "0" ? Or does it  refering to R_0?

It corresponds to the distance dr, where dr is the step between the grid
points. The documentation uses the symbol r0, but this has nothing to do
with the compression radius r0.

You can test it by setting up an H2 molecule with a distance between the
atoms being equal to one of the tabulated grid points and setting
WriteHS=Yes, which would print your H and S matrices. You should see the
same elements as in the SK-table.

> 3.Spline block
>    line4 to 4+nInt-2, what is the unit for nInt? Is it angstrom or
> atomic unit?

See comment 1.

> 
> 4. This is the some part extracted from from mio-1-1/C-C.skf
> 
   i dont understand from line4 to line22, can someone explain to me? I
> thought it was the H and S matrix elements but it seems not because the
> total nGridpoints is 500 ( from line 23 to line 522) and it seems the
> block of H and S matrix elements don't include line4 to line22. Can
> anyone tell me the purpose of line 3 to line22 ?

For historical reasons, integrals were not generated for distances below
0.4 au. Corresponding values are filled up with some arbitrary values,
usually zeros. Note, that in the DFTB, results for atoms getting closer
than 0.4 au are questionable anyway.

  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/


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: OpenPGP digital signature
URL: <http://mailman.zfn.uni-bremen.de/pipermail/dftb-plus-user/attachments/20141112/aacaaf45/attachment.pgp>