[CP2K-user] [CP2K:21802] Mismatch between CP2K computed Force constant (a.u)and Gaussian computed force constant(mDyne/angstrom)

[Naina Sethi]

Dear Prof. Hutter,
Is there any mistake in my input setup? Could you please help.

On Monday, August 25, 2025 at 3:05:15 PM UTC+5:30 Naina Sethi wrote:

> I am using CP2K version 2024.3 and attempted to reproduce one of the 
> sample calculations on the benzene molecule (
> https://www.cp2k.org/exercises:2015_ethz_mmm:infra_red). However, I am 
> unable to obtain force constants similar to those that i get from gaussian. 
> While the vibrational frequencies, IR intensities, and reduced masses agree 
> perfectly with Gaussian results, the force constants differ 
> significantly(specifically for lower frequency regime). This discrepancy is 
> concerning because the magnitude of the force constants is critical for my 
> work. Could you please advise whether this might be related to changes in 
> the code since the example was prepared, or if I might be missing something 
> in my setup?
>
> I am attaching the Input and output files from CP2K and gaussian 
> calculation. Kindly suggest. 
>
> Thank you very much for your time and guidance.
>
> Best regards,
>
>

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