Comment on "Critique of the foundations of time-dependent density functional theory" [Phys. Rev.A. 75, 022513 (2007)]

A recent paper (Phys. Rev A. 75, 022513 (2007), arXiv:cond-mat/0602020) challenges exact time-dependent density functional theory (TDDFT) on several grounds. We explain why these criticisms are either irrelevant or incorrect, and that TDDFT is both formally exact and predictive.Comment: 4 pages; This is a Comment on the paper cited above, also at arXiv:cond-mat/060202

Density functional theory in one-dimension for contact-interacting fermions

A density functional theory is developed for fermions in one dimension, interacting via a delta-function. Such systems provide a natural testing ground for questions of principle, as the local density approximation should work well for short-ranged interactions. The exact-exchange contribution to the total energy is a local functional of the density. A local density approximation for correlation is obtained using perturbation theory and Bethe-Ansatz results for the one-dimensional contact-interacting uniform Fermi gas. The ground-state energies are calculated for two finite systems, the analogs of Helium and of Hooke's atom. The local approximation is shown to be excellent, as expected.Comment: 10 pages, 7 Figure

Identification of two new HMXBs in the LMC: a ∼\sim2013 s pulsar and a probable SFXT

We report on the X-ray and optical properties of two high-mass X-ray binary systems located in the Large Magellanic Cloud (LMC). Based on the obtained optical spectra, we classify the massive companion as a supergiant star in both systems. Timing analysis of the X-ray events collected by XMM-Newton revealed the presence of coherent pulsations (spin period $\sim$2013 s) for XMMU J053108.3-690923 and fast flaring behaviour for XMMU J053320.8-684122. The X-ray spectra of both systems can be modelled sufficiently well by an absorbed power-law, yielding hard spectra and high intrinsic absorption from the environment of the systems. Due to their combined X-ray and optical properties we classify both systems as SgXRBs: the 19$^{\rm th}$ confirmed X-ray pulsar and a probable supergiant fast X-ray transient in the LMC, the second such candidate outside our Galaxy.Comment: 12 pages, 10 figures, accepted for publication in MNRA

Undoing static correlation: Long-range charge transfer in time-dependent density functional theory

Long-range charge transfer excited states are notoriously badly underestimated in time-dependent density functional theory (TDDFT). We resolve how {\it exact} TDDFT captures charge transfer between open-shell species: in particular the role of the step in the ground-state potential, and the severe frequency-dependence of the exchange-correlation kernel. An expression for the latter is derived, that becomes exact in the limit that the charge-transfer excitations are well-separated from other excitations. The exchange-correlation kernel has the task of undoing the static correlation in the ground state introduced by the step, in order to accurately recover the physical charge-transfer states.Comment: 2 figure

Cation Transport in Polymer Electrolytes: A Microscopic Approach

A microscopic theory for cation diffusion in polymer electrolytes is presented. Based on a thorough analysis of molecular dynamics simulations on PEO with LiBF$_4$ the mechanisms of cation dynamics are characterised. Cation jumps between polymer chains can be identified as renewal processes. This allows us to obtain an explicit expression for the lithium ion diffusion constant D_{Li} by invoking polymer specific properties such as the Rouse dynamics. This extends previous phenomenological and numerical approaches. In particular, the chain length dependence of D_{Li} can be predicted and compared with experimental data. This dependence can be fully understood without referring to entanglement effects.Comment: 4 pages, 4 figures, Physical Review Letters in pres

First-Principles Correlated Approach to the Normal State of Strontium Ruthenate

The interplay between multiple bands, sizable multi-band electronic correlations and strong spin-orbit coupling may conspire in selecting a rather unusual unconventional pairing symmetry in layered Sr$_{2}$RuO$_{4}$. This mandates a detailed revisit of the normal state and, in particular, the $T$-dependent incoherence-coherence crossover. Using a modern first-principles correlated view, we study this issue in the actual structure of Sr$_{2}$RuO$_{4}$ and present a unified and quantitative description of a range of unusual physical responses in the normal state. Armed with these, we propose that a new and important element, that of dominant multi-orbital charge fluctuations in a Hund's metal, may be a primary pair glue for unconventional superconductivity. Thereby we establish a connection between the normal state responses and superconductivity in this system.Comment: 8 pages, 4 figure