Is there an anisotropy factor (g factor) for TDDFT absorption and circular dichroism calculations?

Question

Experimentally, anisotropy factor is calculated by dividing the CD (circular dichroism) spectra by the absorbance spectra and multiplying by a factor of 32980 (in order to get a dimensionless quantity).

Theoretical calculations can be performed via TDDFT to obtain rotatory and oscillatory strengths, obtaining excitations for each case and adjusting, for each excitation, a curve, obtaining then the "theoretical absorbance/CD spectra".

How can then we define a theoretical anisotropy factor: Does it make sense? Should another calculation be performed?

Would you divide both adjusted curves or divide the corresponding excitations, adjusting a new set of curves to what you get?

Any clues?

Answer 1

Someone else can probably answer this in more detail, but most software packages allow for simulated spectra to be calculated just as you have said (not just the excitations). You can probably take the spectra and treat it the same as your experimental spectra.

At the very least, I was able to find a recent paper that appears to have done exactly just that.

TD-DFT Analysis of the Dissymmetry Factor in Camphor

Answer 2

Since I just answered this over on chemistry.stackexchange then spotted the question here, I'm going to link it and repeat the essential point.

The method suggested by Tristan is mostly valid, but the more standard approach is to calculate $g_{abs}$ directly as 4 times the ratio of rotational strength (the imaginary part of the dot product of electric and magnetic transition dipole moments) to the dipole strength.