Compute frequency from wavefunction

1

Dear all,

Is the main difference between the wavefunction object obtained from calling frequency()vs. that obtained from energy() that the former also contains harmonic vibrational frequency information?

The following does not work:
E, wfn = energy(level_of_theory, return_wfn=True)
wfn.frequencies.get(0) # wfn.frequencies is NoneType

while this works:
E, wfn = frequency(level_of_theory, return_wfn=True)
wfn.frequencies.get(0) # works as expected

2

You don’t want to calculate the Hessian when you just want an energy. Too expensive. So energy(), gradient(), frequency() will initiate energies, gradients and hessians calculations, respectively. Note that there is also a hessian() function, but you usually want frequencies() to get the vibrational analysis.

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