[CP2K-user] [CP2K:21770] Re: Mismatch between CP2K computed Force constant (a.u)and Gaussian computed force constant(mDyne/angstrom)

[Frederick Stein]

Dear Naina,
Are you sure that all relevant parameters (especially CUTOFF, EPS_DEFAULT, 
EPS_SCF) are well converged? Beware that a vibrational analysis requires 
much tighter thresholds than force calculations. Can you provide your input 
file? How do the frequencies compare between both codes?
Best,
Frederick

Naina Sethi schrieb am Samstag, 23. August 2025 um 16:15:05 UTC+2:

> *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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