Tracing molecular electronic excitation dynamics in real time and space.

We present a method for studying the movement of electrons and energy within and between electronically excited molecules. The dynamically changing state is a many-electron wavepacket, for which we numerically integrate the Schrodinger equation using the ADC(2) effective Hamiltonian for the particle-hole propagator. We develop the tools necessary for following the separate motions of the particles and holes.

Nature of the lowest excited states of neutral polyenyl radicals and polyene radical cations.

Due to the close relation of the polyenyl radicals C(2n+1)H(2n+3) () and polyene radical cations C(2n)H(2n+2) (+) to the neutral linear polyenes, one may suspect their excited states to possess substantial double excitation character, similar to the famous S(1) state of neutral polyenes and thus to be equally problematic for simple excited state theories. Using the recently developed unrestricted algebraic-diagrammatic construction scheme of second order perturbation theory and the equation-of-motion coupled-cluster method, the vertical excitation energies, their corresponding oscillator strengths, and the nature of the wave functions of the lowest excited electronic states of the radicals are calculated and analyzed in detail. For the polyenyl radicals two one-photon allowed states are found as D(1) and D(4) states, with two symmetry-forbidden D(2) and D(3) states in between, while in the polyene radical cations D(1) and D(2) are allowed and D(3) is forbidden.

Unrestricted algebraic diagrammatic construction scheme of second order for the calculation of excited states of medium-sized and large molecules.

An unrestricted version of the algebraic diagrammatic construction (ADC) scheme of the polarization propagator in second order perturbation theory [UADC(2)] is derived via the intermediate state representation. The accuracy of the extended UADC(2)-x approach is evaluated by comparison of computed excitation energies of 11 medium-sized radicals with their corresponding experimental literature values and with excitation energies computed at equation-of-motion-CCSD (coupled clusters singles and doubles) level of theory. Overall, our numerical tests show that UADC(2)-x exhibits an averaged mean deviation in the excitation energies of only 0.

Identification of an additional low-lying excited state of carotenoid radical cations.

Carotenoids are the crucial pigments involved in photoprotection and in scavenging harmful free radicals in all living organisms. The underlying chemical processes are charge transfer and free radical reactions, both of them leading to carotenoid radical cation (Car*+) formation. Accurate knowledge of the molecular properties of Car*+ is thus a prerequisite for understanding of their function as photoprotective and antioxidant agents.