prefactor_opa

psi4.driver.p4util.prefactor_opa()

Prefactor for converting microscopic observable to decadic molar extinction coefficient in one-photon absorption.

Return type:

float

Notes

This function implements the calculation of the following prefactor:

$$k=\frac{4{\pi }^2{N}_{\mathrm{A}}}{3\times 1000\times \ln (10)(4\pi {ϵ}_0)n\hslash c}$$

The prefactor is computed in SI units and then adjusted for the fact that we use atomic units to express microscopic observables: excitation energies and transition dipole moments. The refractive index $n$ is, in general, frequency-dependent. We assume it to be constant and equal to 1.