Core hole-electron correlation in coherently coupled molecules

Towards Understanding Excited-State Properties of Organic Molecules Using Time-Resolved Soft X-ray Absorption Spectroscopy

The extension of the pump-probe approach known from UV/VIS spectroscopy to very short wavelengths together with advanced simulation techniques allows a detailed analysis of excited-state dynamics in organic molecules or biomolecular structures on a nanosecond to femtosecond time level. Optical pump soft X-ray probe spectroscopy is a relatively new approach to detect and characterize optically dark states in organic molecules, exciton dynamics or transient ligand-to-metal charge transfer states. In this paper, we describe two experimental setups for transient soft X-ray absorption spectroscopy based on an LPP emitting picosecond and sub-nanosecond soft X-ray pulses in the photon energy range between 50 and 1500 eV. We apply these setups for near-edge X-ray absorption fine structure (NEXAFS) investigations of thin films of a metal-free porphyrin, an aggregate forming carbocyanine and a nickel oxide molecule. NEXAFS investigations have been carried out at the carbon, nitrogen and oxygen K-edge as well as on the Ni L-edge. From time-resolved NEXAFS carbon, K-edge measurements of the metal-free porphyrin first insights into a long-lived trap state are gained. Our findings are discussed and compared with density functional theory calculations.

Laboratory quick near edge x-ray absorption fine structure spectroscopy in the soft x-ray range with 100 Hz frame rate using CMOS technology

In laboratory based x-ray absorption fine structure (XAFS) spectroscopy, the slow readout speed of conventional CCD cameras can prolong the measuring times by multiple orders of magnitude. Using pulsed sources, e.g., laser-based x-ray sources, the pulse repetition rate often exceeds the frame rate of the CCD camera. We report the use of a scientific CMOS (sCMOS) camera for XAFS spectroscopy with a laser-produced plasma source facilitating measurements at 100 Hz. With this technological improvement, a new class of experiments becomes possible, starting from the time consuming analysis of samples with small absorption to pump-probe investigations. Furthermore, laboratory quick soft x-ray absorption fine structure (QXAFS) measurements with 10 ms time resolution are rendered feasible. We present the characterization of the sCMOS camera concerning noise characteristics and a comparison to conventional CCD camera performance. The feasibility of time resolved QXAFS measurements is shown by analyzing the statistical uncertainty of single shot spectra. Finally, XAFS spectroscopy on a complex sandwich structure with minute amounts of NiO exemplifies the additional merits of fast detectors.

New and Efficient Implementation of CC3

We present a new and efficient implementation of the closed shell coupled cluster singles and doubles with perturbative triples method (CC3) in the electronic structure program eT. Asymptotically, a ground state calculation has an iterative cost of 4nV4nO3 floating point operations (FLOP), where nV and nO are the number of virtual and occupied orbitals, respectively. The Jacobian and transpose Jacobian transformations, required to iteratively solve for excitation energies and transition moments, both require 8nV4nO3 FLOP. We have also implemented equation of motion (EOM) transition moments for CC3. The EOM transition densities require recalculation of triples amplitudes, as nV3nO3 tensors are not stored in memory. This results in a noniterative computational cost of 10nV4nO3 FLOP for the ground state density and 26nV4nO3 FLOP per state for the transition densities. The code is compared to the CC3 implementations in CFOUR, DALTON, and PSI4. We demonstrate the capabilities of our implementation by calculating valence and core excited states of l-proline.