Numerical differentiation method to calculate molecular properties at ground and excited states - Application to Julolidinemalononitrile

A general method to evaluate the Cartesian derivatives of the dipole moment and polarizability of electronic excited states is presented. This method, based on successive numerical differentiations of the dipole moment, is implemented in a locally developed package of programs called VibKit. An application to describe the vibrational signatures of the first excited state of julolidinemalononitrile in comparison to those of its ground state has been performed using time-dependent density functional theory (TDDFT). The modifications of the IR and Raman signatures are shown to be related to the delocalization of the charge density and geometry modifications upon excitation, as evidenced by the use of group coupling matrices (GCMs).