[DFTB-Plus-User] Identity overlap matrix

[Bálint Aradi]

Dear Daniel,

The two options Jacek pointed out, are indeed possibilities to obtain
unity overlap. They have the side effect, though, that your non-SCC
Hamiltonian also reduces to a diagonal matrix with the free atomic
eigenvalues on its diagonal.

If you want to keep the Hamiltonian, and only zero out the non-diagonal
elements of the overlap, you may achieve it by changing the SK-files and
zero out all overlap integrals. Those are usually the last 10 columns in
the integral table, see more in the format description:

https://dftb.org/fileadmin/DFTB/public/misc/slakoformat.pdf

You can then use the WriteHS option to check, whether your H/S have the
desired form. And, of course, please use the modified SK-tables only for
the sake your tests, and not use them for production purposes!

Best regards,

Bálint


On 23.06.22 21:27, Jacek Jakowski wrote:
> You can achieve that without any change in source following one of
> these options:  
> (1) you need to spread your atoms sufficiently  apart. You may want to
> check the cutoff in Slater-Koster table to  when the overlaps become
> zero (or are close enough to zero)
> (2)  You can modify your Slater-Koster files  and set all  overlap
> parameters  to zero.
> 
> Of course, you can modify the code too, but I don't think it is
> worth the effort.
> 
> Jacek
> 
> 
> 
> 
> 
> On Thu, Jun 23, 2022 at 2:46 PM Daniel A Lemus <dlemus at purdue.edu
> <mailto:dlemus at purdue.edu>> wrote:
> 
>     Hello,
> 
>     My group is interfacing DFTB+ with our code and we need to test a
>     specific scenario in which the overlap matrix is an identity matrix.
>     Is there a way to achieve this through the API or a source code change?
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-- 
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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