[DFTB-Plus-User] IR intensity

Moyassar Meshhal moyassar.meshhal at uni-rostock.de
Wed Apr 15 22:37:38 CEST 2020


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
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