[DFTB-Plus-User] Excited State calculation: Multiple StateOfInterest and format of TRA.DAT

[Ben Hourahine]

Hello Dirk,

at the moment calculation of charges for multiple states simultaneously
is missing (I'll add it to the feature request list).

Could I ask what you are calculating that needs this data? If if is for
multiple excited states in a spectra (for example plasmonic features),
the Casida approach might not be the most efficient way to obtain this
information (there may be something in the 18.1 release in this
direction, based on coupled perturbed or Sternheimer equations).

The reason for the behaviour in the TRA.DAT is due (probably) to
symmetry in your system. What is printed is the dominant single particle
transition contributing to the many particle excited states. But as a
result of degeneracy in a group of single particle states, the relative
unitary transformation of the single particle states is undefined. The
eigensolver has chosen a set of degenerate vectors such that the same
single particle excitation occurs in multiple degenerate many particle
transformations.

In principle, it would be possible to choose a unitary transformation
such that the single particle transition only contributes in one of
these transitions, but this would not change the energy of the
transitions, only the relative dipole intensities within the degenerate
many particle transitions.

If you notice, sum(Weight^2) over the degenerate group = 1. At some
point there might be a change in the output of DFTB+ to show the sum and
degeneracy of transitions in these cases, instead of the individual
transitions.

If you would like me to investigate further, you can send the input off
list.

Regards

Ben


On 28/06/17 15:49, Dirk Ziemann wrote:
> Dear all,
>
> I have two questions concerning the excited state calculation.
>
> I am interested in the Mulliken charges of many different excited
> states. If I specify a single state of interest at StateOfInterest
> everything works fine, but there is an error for multiple numbers. Is it
> possible to get the Mulliken charges for many different states at
> once?            (I need >1000 states)
>
> In my TRA.DAT files I see the following lines (see below). Why does a
> transition appears multiple times?
>
> As far as I have checked it, this happens only to the first transition.I
> have a feeling that it is related to the value of OscillatorWindow. If I
> choose a high value this does not happen. The smaller the value the
> higher the number of "multiple first transitions".
>
>
> Thank you for your help and best wishes   Dirk
>
>
> everything the same in dftb_in.hsd except the  ExcitedState-part
>
> example 1:
>
>   Energy      1          3.625 eV   S
>
>   Transition         Weight       KS [eV]
>  =============================================
> 13723   -> 13908     0.7361       4.616
> 13723   -> 13908     0.5047       4.616
> 13723   -> 13908     0.3897       4.616
> 13723   -> 13908     0.2272       4.616
>  1011   -> 20029     0.0000      39.368
>  1011   -> 20028     0.0000      39.368
>
> dftb_in.hsd
>
> ExcitedState {
>     Casida {
>         NrOfExcitations = 100
>         StateOfInterest = 0
>         Symmetry = singlet
>         OscillatorWindow = 1E-1
>         WriteStatusArnoldi = Yes
>         WriteTransitions = Yes
>    }
> }
>
> //==============================================//
>
> example 2
>
>   Energy      1          3.754 eV   S
>
>   Transition         Weight       KS [eV]
>  =============================================
> 13749   -> 13754     0.8301       3.754
> 13749   -> 13754     0.4022       3.754
> 13749   -> 13754     0.3398       3.754
> 13749   -> 13754     0.1559       3.754
> 13749   -> 13754     0.0687       3.754
> 13749   -> 13754     0.0550       3.754
> 13749   -> 13754     0.0417       3.754
>   215   -> 20033     0.0000      39.768
>   215   -> 20035     0.0000      39.768
>
> dftb_in.hsd
>
> ExcitedState {
>     Casida {
>         NrOfExcitations = 30
>         StateOfInterest = 0
>         Symmetry = singlet
>         OscillatorWindow = 1E-2
>         WriteStatusArnoldi = Yes
>         WriteTransitions = Yes
>    }
> }
>
>
>

-- 
      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