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frequency(name[, func, dertype, irrep, molecule])[source]

Function to compute harmonic vibrational frequencies.

Aliases :frequencies(), freq()
Returns:(float) Total electronic energy in Hartrees.


Analytic hessians are not available. Frequencies will proceed through finite differences according to availability of gradients or energies.


Some features are not yet implemented. Buy a developer a coffee.

  • Make frequency look analogous to gradient, especially in matching derivative levels. Make dertype actually a dertype type.
  • name (string) –

    'scf' || 'df-mp2' || 'ci5' || etc.

    First argument, usually unlabeled. Indicates the computational method to be applied to the system.

  • dertype (dertype) –

    \Rightarrow 'hessian' \Leftarrow || 'gradient' || 'energy'

    Indicates whether analytic (if available- they’re not), finite difference of gradients (if available) or finite difference of energies is to be performed.

  • irrep (int or string) –

    \Rightarrow -1 \Leftarrow || 1 || 'b2' || 'App' || etc.

    Indicates which symmetry block (Cotton ordering) of vibrational frequencies to be computed. 1, '1', or 'a1' represents a_1, requesting only the totally symmetric modes. -1 indicates a full frequency calculation.

  • molecule (molecule) –

    h2o || etc.

    The target molecule, if not the last molecule defined.

Examples :
>>> # [1] <example description>
>>> <example python command>
>>> # [2] Frequency calculation for b2 modes through finite difference of gradients
>>> frequencies('scf', dertype=1, irrep=4)

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