I am following the computational method described in Scientific Reports.[1] Where the authors analyze the contribution of each excited state normal-modes to the shift of the transition energy. For this calculation they use the force constants of each normal mode.
I am using ORCA but could not understand how to generate the force constants. I did find that the orca_vib program generates force constants, but I did not find how to use the output to generate a force constant for the specific normal modes.

I also found this question,[2] I am not sure if it solves my problem. I saw the great answer by Jan Jensen who following the equation: $$\tilde{\nu}=\sqrt{k_i^{\prime\prime}}/(2\pi \times 137 \times 5.29\times 10^{-9}).$$ Do I just need to plug in my vibrational frequencies and rearrange the equation to get $k$?


  1. Schweighöfer, F.; Dworak, L.; Braun, M.; Zastrow, M.; Wahl, J.; Burghardt, I.; Rück-Braun, K.; Wachtveitl, J. Vibrational coherence transfer in an electronically decoupled molecular dyad. Sci. Rep. 2015, 5 (1), No. 9368. DOI: 10.1038/srep09368.
  2. How to calculate wavenumbers of normal modes from the eigenvalues of the Cartesian force constant matrix?


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