Computations of the Raman optical activity via the sum‐over‐states expansions

A computationally convenient and reasonably accurate scheme of computation of the Raman Optical Activity (ROA) is presented and tested on model examples. Electromagnetic tensors were obtained using the sum-over-states (SOS) methodology, while their nuclear derivatives were estimated through numerical differentiation. An origin dependence of the results was overcome by a distributed origin gauge transformation. Becke-3LYP functional and corresponding Kohn–Sham orbitals are used for the excited states. The method was compared to a benchmark coupled-perturbed (CP) calculation on formamide and a standard ROA spectral simulation and experiment for α-pinene. Spectra of four standard peptide conformations (α-helix, 310-helix, coil, and β-sheet) were simulated with smaller fragments and compared to previous experimental observations.