mixed derivatives during vibrational analysis

[Dr. Sandeep Kumar Reddy]

Hi All,

I am wondering how mixed derivatives are computed for the hessian matrix 
during vibrational analysis? cp2k output tells that it calculates energies 
by displacing variables one at a time, but the formulae show two variables 
should be displaced at each time to compute them. Thanks for your help.

Sandeep 

 
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