[CP2K-user] [CP2K:21774] Mismatch between CP2K computed Force constant (a.u)and Gaussian computed force constant(mDyne/angstrom)

[Jürg Hutter]

Hi
Are you using a newer version of CP2K (2023.1 or later)? If not, please update your version.
If yes, please send an example input and output file in order to reproduce the problem.

regards
JH

________________________________________
From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Naina Sethi <sethinaina336 at gmail.com>
Sent: Saturday, August 23, 2025 4:15 PM
To: cp2k
Subject: [CP2K:21769] Mismatch between CP2K computed Force constant (a.u)and Gaussian computed force constant(mDyne/angstrom)

Dear all,
I am working on calculating the vibrational frequencies and force constants of a water molecule. In CP2K, the force constants are reported in atomic units (Hartree/Bohr²), while Gaussian lists them in mDyne/Å. The conversion factor between Hartree/Bohr² and mDyne/Å is about 15.57. However, even after applying this factor, the results from CP2K do not match the force constant values reported by Gaussian. Could anyone clarify why this discrepancy occurs?

       Frc consts --           1.7016                   8.9360               9.7649        (gaussian)
VIB|Frc consts (a.u.)    0.017668               0.567398         0.663392     (CP2K)

Thanks and Regards
Naina

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