Time-dependent density-functional theory beyond the local-density approximation

Optical Absorptions of New Blue-Light Emitting Oligoquinolines Bearing Pyrenyl and Triphenyl Endgroups Investigated with Time-Dependent Density Functional Theory

The optical absorption spectra of a family of four n-type conjugated oligomers, oligoquinolines, which can be commercially used to develop high-performance light-emitting diodes for their many desirable properties, have been recently calculated from time-depedent density functional theory (TDDFT) within the adiabatic approximation for the dynamical exchange-correlation potential. In this work, we investigate the optical absorption of two new family members of the blue-light emitting oligoquinolines bearing pyrenyl and triphenyl endgroups in gas phase and chloroform (CHCl3) solution employing the adiabatic TDDFT. The ionization potentials and electron affinities of these two oligoquinoline molecules are also calculated with the ground-state DFT, from which the adiabatic dynamical exchange-correlation potential is constructed. We show that the calculated optical absorptions are in good agreement with experiments. The ionization potentials obtained with the DFT methods agree well with the experimental estimates, while the electron affinities are significantly underestimated in comparison with experiments. A natural transition orbital analysis for selected excited states with the largest oscillator strengths shows that the electronic charge is slightly redistributed in the process of electronic excitations.

Current density partitioning in time-dependent current density functional theory

We adapt time-dependent current density functional theory to allow for a fragment-based solution of the many-electron problem of molecules in the presence of time-dependent electric and magnetic fields. Regarding a molecule as a set of non-interacting subsystems that individually evolve under the influence of an auxiliary external electromagnetic vector-scalar potential pair, the partition 4-potential, we show that there are one-to-one mappings between this auxiliary potential, a sharply-defined set of fragment current densities, and the total current density of the system. The partition electromagnetic (EM) 4-potential is expressed in terms of the real EM 4-potential of the system and a gluing EM 4-potential that accounts for exchange-correlation effects and mutual interaction forces between fragments that are required to yield the correct electron dynamics. We prove the zero-force theorem for the fragmented system, establish a variational formulation in terms of action functionals, and provide a simple illustration for a charged particle in a ring.

Prediction of Excitation Energies for Conjugated Oligomers and Polymers from Time-Dependent Density Functional Theory

With technological advances, light-emitting conjugated oligomers and polymers have become competitive candidates in the commercial market of light-emitting diodes for display and other technologies, due to the ultralow cost, light weight, and flexibility. Prediction of excitation energies of these systems plays a crucial role in the understanding of their optical properties and device design. In this review article, we discuss the calculation of excitation energies with time-dependent density functional theory, which is one of the most successful methods in the investigation of the dynamical response of molecular systems to external perturbation, owing to its high computational efficiency.