The Long Journey from Ab Initio Calculations to Density Functional Theory for Nuclear Large Amplitude Collective Motion

At present there are two vastly different ab initio approaches to the description of the the many-body dynamics: the Density Functional Theory (DFT) and the functional integral (path integral) approaches. On one hand, if implemented exactly, the DFT approach can allow in principle the exact evaluation of arbitrary one-body observable. However, when applied to Large Amplitude Collective Motion (LACM) this approach needs to be extended in order to accommodate the phenomenon of surface-hoping, when adiabaticity is strongly violated and the description of a system using a single (generalized) Slater determinant is not valid anymore. The functional integral approach on the other hand does not appear to have such restrictions, but its implementation does not appear to be straightforward endeavor. However, within a functional integral approach one seems to be able to evaluate in principle any kind of observables, such as the fragment mass and energy distributions in nuclear fission. These two radically approaches can likely be brought brought together by formulating a stochastic time-dependent DFT approach to many-body dynamics.Comment: 9 page

Some open questions in TDDFT: Clues from Lattice Models and Kadanoff-Baym Dynamics

Two aspects of TDDFT, the linear response approach and the adiabatic local density approximation, are examined from the perspective of lattice models. To this end, we review the DFT formulations on the lattice and give a concise presentation of the time-dependent Kadanoff-Baym equations, used to asses the limitations of the adiabatic approximation in TDDFT. We present results for the density response function of the 3D homogeneous Hubbard model, and point out a drawback of the linear response scheme based on the linearized Sham-Schl\"uter equation. We then suggest a prescription on how to amend it. Finally, we analyze the time evolution of the density in a small cubic cluster, and compare exact, adiabatic-TDDFT and Kadanoff-Baym-Equations densities. Our results show that non-perturbative (in the interaction) adiabatic potentials can perform quite well for slow perturbations but that, for faster external fields, memory effects, as already present in simple many-body approximations, are clearly required.Comment: 15 pages, submitted to Chemical Physic

The electronic structure of iridium oxide electrodes active in water splitting

Iridium oxide based electrodes are among the most promising candidates for electrocatalyzing the oxygen evolution reaction, making it imperative to understand their chemical/electronic structure. However, the complexity of iridium oxide's electronic structure makes it particularly difficult to experimentally determine the chemical state of the active surface species. To achieve an accurate understanding of the electronic structure of iridium oxide surfaces, we have combined synchrotron-based X-ray photoemission and absorption spectroscopies with ab initio calculations. Our investigation reveals a pre-edge feature in the O K-edge of highly catalytically active X-ray amorphous iridium oxides that we have identified as O 2p hole states forming in conjunction with IrIII. These electronic defects in the near-surface region of the anionic and cationic framework are likely critical for the enhanced activity of amorphous iridium oxides relative to their crystalline counterparts

Femtosecond near-infrared laser pulses elicit generation of reactive oxygen species in mammalian cells leading to apoptosis-like death.

Two-photon excitation-based near-infrared (NIR) laser scanning microscopy is currently emerging as a new and versatile alternative to conventional confocal laser scanning microscopy, particularly for vital cell imaging in life sciences. Although this innovative microscopy has several advantages such as highly localized excitation, higher penetration depth, reduced photobleaching and photodamage, and improved signal to noise ratio, it has, however, recently been evidenced that high-power NIR laser irradiation can drastically inhibit cell division and induce cell death. In the present study we have investigated the cellular responses of unlabeled rat kangaroo kidney epithelium (PtK2) cells to NIR femtosecond laser irradiation. We demonstrate that NIR 170-fs laser pulses operating at 80-MHz pulse repetition frequency and at mean power of > or = 7 mW evoke generation of reactive oxygen species (ROS) such as H2O2 that can be visualized in situ by standard in vivo cytochemical analysis using Ni-3,3'-diaminobenzidine (Ni-DAB) as well as with a recently developed fluorescent probe Jenchrom px blue. The formation of the Ni-DAB reaction product as well as that of Jenchrom was relatively more pronounced when irradiated cells were incubated in alkaline solution (pH 8) than in those incubated in acidic solution (pH 6), suggesting peroxisomal localization of these reaction products. Two-photon time-lapse imaging of the internalization of the cell impermeate fluorescent dye propidium iodide revealed that the integrity of the plasma membrane of NIR irradiated cells is drastically compromised. Visualization of the nuclei with DNA-specific fluorescent probes such as 4',6-diamidino-2-phenylindole 24 h postirradiation further provided tangible evidence that the nuclei of these cells undergo several deformations and eventual fragmentation. That these NIR irradiated cells die by apoptosis has been established by in situ detection of DNA strand breaks using the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling method. Because the reactive oxygen species such as H2O2 and OH* can cause noxious effects such as cell membrane injury by peroxidation of polyunsaturated lipids and proteins and oxidative phosphorylation, and alterations of ATP-dependent Ca2+ pumps, these ROS are likely to contribute to drastic cytological alterations observed in this study following NIR irradiation. Taken together, we have established that NIR laser irradiations at mean power > or = 7 mW delivered at pulse duration time of 170 fs generally used in two- and multiphoton microscopes cause oxidative stress (1) evoking production of ROS, (2) resulting in membrane barrier dysfunction, (3) inducing structural deformations and fragmentation of the nuclei as well as DNA strand breaks, (4) leading to cell death by apoptosis