Linear response calculations of molecular optical and magnetic properties using program RPAC: NMR shielding tensors of pyridine and n-azines

Abstract

The theory of the linear response of a single-determinant wavefunction and the associated molecular properties is reviewed briefly, and the current status of the RPAC molecular properties program system is described. The program is capable of calculating electronic excitation energies and intensities and of various analyses of the nature of the excitations with the aid of localized molecular orbitals. In addition, nuclear magnetic shielding tensors can be computed and analyzed in a localized orbital framework. As an example of the program's present capabilities, we present calculations of the nuclear shielding tensors of a series of six-membered aromatic compounds containing one or more nitrogen atoms in the localized orbital-local origin (LORG) method, using extended basis sets. The properties of the shieldings are discussed with the aid of a novel scheme for visualization of tensorial properties.