[DFTB-Plus-User] IR intensity

[DFTB Software]

dear Moyassr

I am also interested in it!

it is a first guess:

DFTB+ uses Energy to calculate Hessian by using numerical differentiation.
So in principle all the dipole moments of the displaced geometry are either
saved or if not, by simple editing of the source file it can be saved.

These information can used to make rate of change of the dipolemoment w.r.t
vibrational modes. I think you have to use mass weighted coordinates of the
normal modes in the differentiation procedure.

Mohan


On Thu, 16 Apr 2020 at 02:07, Moyassar Meshhal via DFTB-Plus-User <
dftb-plus-user at mailman.zfn.uni-bremen.de> wrote:

> Dear dftb+ users,
>
> I am trying to calculate IR spectra using dftb+.
> I did the following steps:
> 1- geometry optimization.
> 2- second derivative calculation (to get hessian)
> 3- hessian diagonalization to calculate the normal modes (using the modes
> tool).
>
> However, I still need the intensities to plot the spectra.
>
> In a paper in which the authors utilized dftb+ in calculating IR spectra
> of a system related to my work I read the following statement:
>
> "*The IR intensity for a certain vibrational mode was proportional to
> square of the variation of dipole moment from the ground-state geometry to
> a structure with the normalized vibrational eigenvector superimposed*."
>
> I couldn't find the dipole moments in the output files generated during
> the above mentioned steps, so my question is:
> Should I calculate the dipole moments of both the ground-state structure
> and the vibrational structure for each normal modes? or They are already
> calculated?
>
> Best Regards
> Moyassar
> _______________________________________________
> DFTB-Plus-User mailing list
> DFTB-Plus-User at mailman.zfn.uni-bremen.de
> https://mailman.zfn.uni-bremen.de/cgi-bin/mailman/listinfo/dftb-plus-user
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.zfn.uni-bremen.de/pipermail/dftb-plus-user/attachments/20200418/ffa871b3/attachment.htm>