A molecular orbital selection approach for fast calculations of specific rotation with density functional theory

In this work, we describe a simple approach to select the most important molecular orbitals (MOs) to compute the optical rotation tensor through linear response (LR) Kohn-Sham density functional theory (KS-DFT). Taking advantage of the iterative nature of the algorithms commonly used to solve the LR equations, we select the MOs with contributions to the guess perturbed density that are larger than a certain threshold and solve the LR equations with the selected MOs only. We propose two criteria for the selection, and two definitions of the selection threshold. We then test the approach with two functionals (B3LYP and CAM-B3LYP) and two basis sets (aug-cc-pVDZ and aug-cc-pVTZ) on a set of 51 organic molecules with specific rotation spanning five orders of magnitude, 10⁰ -10⁴ deg (dm^-1 (g/mL)^-1 ). We show that this approach indeed can provide very accurate values of specific rotation with estimated speedup that ranges from 2 to 8× with the most conservative selection criterion, and up to 20 to 30× with the intermediate criterion.