The excitation scheme: A new method for calculation of vibrational circular dichroism spectra

An alternate procedure for calculating vibrational circular dichroism is proposed. The method eliminates the need to solve the magnetically perturbed SCF equations which leads to an overall decrease in computer time. Instead, an expansion over electronic excited states is partially used to estimate the molecular response to the magnetic field and nuclear displacements. A rigid orbital approximation is used for the electronic states. The rotational strengths obtained in this manner are compared to original experimental data for camphor and $\alpha$ -pinene, and previous calculations on propylene oxide and oxirane. In all cases good agreement of simulated spectral intensities with experiment is observed. Although extensive approximations had to be adopted in the current implementation, the excitation scheme yields results superior to those obtained by the classical MFP or VCT formulations of VCD for camphor and $\alpha$ -pinene, whereas MFP/GIAO theory performs better in the case of oxirane.