Photoabsorption Cross-Sections — Nuclear Ensemble Approach
A Python workflow to compute photoabsorption cross-sections, with the nuclear ensemble approach (NEA). An ensemble of nuclear geometries is sampled from the ground-state vibrational (Wigner) distribution, vertical excitation energies and oscillator strengths are evaluated at each geometry with high-level electronic-structure methods (TD-DFT, EOM-CCSD, MRCI+Q and CASPT2), and the broadened transitions are averaged to give σ(λ) with realistic band shapes and widths. We use it to predict UV–Vis spectra and photolysis rates for atmospheric and astrochemical species.
Pipeline: geometry optimization → harmonic frequencies → Wigner sampling → vertical excitation energies & oscillator strengths → data extraction → cross-section convolution & plotting.
