Spectroscopic Constants for Diatomics

Code author: Andrew C. Simmonett

anharmonicity(rvals, energies)

Generates spectroscopic constants for a diatomic molecules. Fits a diatomic potential energy curve using either a 5 or 9 point Legendre fit, locates the minimum energy point, and then applies second order vibrational perturbation theory to obtain spectroscopic constants. The r values provided must bracket the minimum energy point, or an error will result.

A dictionary with the following keys, which correspond to spectroscopic constants, is returned:

Parameters:

• rvals (list) – The bond lengths (in Angstrom) for which energies are provided of length either 5 or 9 but must be the same length as the energies array
• energies (list) – The energies (Eh) computed at the bond lengths in the rvals list

Returns:

(dict) Keys: “re”, “r0”, “we”, “wexe”, “nu”, “ZPVE(harmonic)”, “ZPVE(anharmonic)”, “Be”, “B0”, “ae”, “De” corresponding to the spectroscopic constants in cm-1