[DFTB-Plus-User] overlap between two MD frames

[Ben Hourahine]

Hello Sharma,

the nearest thing to a quick hack would be to calculate the overlap for
a geometry mid-way between the two cases. If the two geometries are
sufficiently close together, then this should be the leading term in the
series expansion of the overlap. The code can write out the overlap
matrix to disc for a specified geometry (WriteHS keyword).

If you need to actually calculating the overlap, there may be a problem
if the atomic displacements are small. Many of the SK files only contain
overlap data beyond a short distance out from the nucleus, so cannot be
used to calculate overlaps between orbitals for less than this distance
(usually several rows of value 0 appear at the start of the SK file in
this case). This would stop you from being able to calculate the overlap
between orbitals on the same atom.

To actually calculate the overlaps, assuming the displacements are large
enough, an external hack would be to
1) construct a geometry with both the atoms at the original and
displaced geometries together
2) Call the code with WriteHS, and take the block of the overlap matrix
associated with overlaps between the two sets of atoms

You might have to remove the tests for atoms being on top of each other
in this case. In principle this could be done inside of the code, but as
you've notice this involves calling several routines, if you do want to
do this I can offer some guidance.

Regards

Ben


On 04/10/16 15:29, Sharma SRK Chaitanya Yamijala wrote:
> Dear Ben,
>
> Thank you for your quick response. I am interested in calculating the
> overlap between atomic orbitals of one frame with the atomic orbitals
> of the other. 
> Sij = < Xi | Xj >,
> Xi = 1st frame atomic orbitals 
> Xj = 2nd frame atomic orbitals
>
> Thanking you again for your quick response,
> Sincerely,
> Sharma.
>
>
>
>
>
> --------------------------------------------------------------------
> Sharma
> http://www.chem.rochester.edu/groups/huo/people/
>
>
> On Tue, Oct 4, 2016 at 10:24 AM, Ben Hourahine
> <benjamin.hourahine at strath.ac.uk
> <mailto:benjamin.hourahine at strath.ac.uk>> wrote:
>
>     Hello Sharma,
>
>     what sort of overlap are you trying to calculate, positional
>     similarity, wavefunction overlap or something else?
>
>     Regards
>
>     Ben
>
>
>     On 04/10/16 15:12, Sharma SRK Chaitanya Yamijala wrote:
>>     Dear all,
>>
>>     Is there any simple hack to calculate the overlap between two
>>     frames using DFTB+. I have gone through the source code and I
>>     found that it is dependent on many modules in lib_dftb
>>     like non-scc.f90, sk.f90, slako_cont.f90 ... and also on the
>>     lib_math modules like sort.f90, bisection.f90 (while calculating
>>     neighbor lists) etc. Any suggestion, please? 
>>
>>     Thank you for your help,
>>     Sincerely,
>>     Sharma.
>>
>>
>>
>>
>>     --------------------------------------------------------------------
>>     Sharma
>>     http://www.chem.rochester.edu/groups/huo/people/
>>     <http://www.chem.rochester.edu/groups/huo/people/>
>>
>>
>>
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>
>     -- 
>           Dr. B. Hourahine, SUPA, Department of Physics,
>         University of Strathclyde, John Anderson Building,
>                 107 Rottenrow, Glasgow G4 0NG, UK.
>         +44 141 548 2325 <tel:%2B44%20141%20548%202325>, benjamin.hourahine at strath.ac.uk
>     <mailto:benjamin.hourahine at strath.ac.uk>
>
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>           2012/13 THE Awards UK University of the Year
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>        The University of Strathclyde is a charitable body,
>             registered in Scotland, number SC015263
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-- 
      Dr. B. Hourahine, SUPA, Department of Physics,
    University of Strathclyde, John Anderson Building,
            107 Rottenrow, Glasgow G4 0NG, UK.
    +44 141 548 2325, benjamin.hourahine at strath.ac.uk

2013/4 THE Awards Entrepreneurial University of the Year
      2012/13 THE Awards UK University of the Year

   The University of Strathclyde is a charitable body,
        registered in Scotland, number SC015263
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