Origin-Independent Sum Over States Simulations of Magnetic and Electronic Circular Dichroism Spectra via the Localized Orbital/Local Origin Method

Although electronic and magnetic circular dichroism (ECD, MCD) spectra reveal valuable details about molecular geometry and electronic structure, quantum-chemical simulations significantly facilitate their interpretation. However, the simulated results may depend on the choice of coordinate origin. Previously (Stepanek and Bou, J. Comput. Chem. 2013, 34, 1531), the sum-over-states (SOS) methodology was found useful for efficient MCD computations. Approximate wave functions were resolved using time-dependent density functional theory, and the origin-dependence was avoided by placing the origin to the center of mass of the investigated molecule. In this study, a more elegant way is proposed, based on the localized orbital/local origin (LORG) formalism, and a similar approach is also applied to generate ECD intensities. The LORG-like approach yields fully origin-independent ECD and MCD spectra. The results thus indicate that the computationally relatively cheap SOS simulations open a new way of modeling molecular properties, including those involving the origin-dependent magnetic dipole moment operator. (c) 2015 Wiley Periodicals, Inc.