Possible bug in reported force constants after vibrational analysis

Leopold Talirz leopold... at gmail.com
Sun May 25 21:33:06 UTC 2014

Dear Matthias,

thank you very much for your quick reply.
I am really not well familiar with normal mode analysis (nor its 
implementation), so please tell me if I am talking nonsense, but I thought 
the eigenvalues of the Hessian were proportional to konst instead of 

At least with the naive definition of a force constant that I am familiar 
with, i.e. you have a potential like U=1/2 * konst * x^2

Or, in other words, could you please direct me to a reference/book that I 
should read to understand how the force constants are defined in CP2K?

Thank you very much!


On Sunday, May 25, 2014 12:38:17 PM UTC+2, Matthias Krack wrote:
> Hi Leopold,
> I think the code is correct, since the eigenvalues epsilon of the Hessian 
> returned in H_eigval2 after its diagonalisation are equivalent to 
> SQRT(konst/rmass). The frequencies, however, are proportional to 
> SQRT(epsilon), i.e. SQRT(H_eigval2).
> Matthias
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