Frequency¶

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

Function to compute harmonic vibrational frequencies.

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

Note

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

Caution

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.

Parameters:

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)