On a method to calculate conductance by means of the Wigner function: two critical tests

We have implemented the linear response approximation of a method proposed to compute the electron transport through correlated molecules based on the time-independent Wigner function [P. Delaney and J. C. Greer, \prl {\bf 93}, 36805 (2004)]. The results thus obtained for the zero-bias conductance through quantum dot both without and with correlations demonstrate that this method is either quantitatively nor qualitatively able to provide a correct physical escription of the electric transport through nanosystems. We present an analysis indicating that the failure is due to the manner of imposing the boundary conditions, and that it cannot be simply remedied.Comment: 22 pages, 7 figur

Algorithm for Linear Response Functions at Finite Temperatures: Application to ESR spectrum of s=1/2 Antiferromagnet Cu benzoate

We introduce an efficient and numerically stable method for calculating linear response functions $\chi(\vec{q},\omega)$ of quantum systems at finite temperatures. The method is a combination of numerical solution of the time-dependent Schroedinger equation, random vector representation of trace, and Chebyshev polynomial expansion of Boltzmann operator. This method should be very useful for a wide range of strongly correlated quantum systems at finite temperatures. We present an application to the ESR spectrum of s=1/2 antiferromagnet Cu benzoate.Comment: 4 pages, 4 figure

Itinerant ferromagnetism in half-metallic CoS_2

We have investigated electronic and magnetic properties of the pyrite-type CoS_2 using the linearized muffin-tin orbital (LMTO) band method. We have obtained the ferromagnetic ground state with nearly half-metallic nature. The half-metallic stability is studied by using the fixed spin moment method. The non-negligible orbital magnetic moment of Co 3d electrons is obtained as $\mu_L = 0.06 \mu_B$ in the local spin density approximation (LSDA). The calculated ratio of the orbital to spin angular momenta / = 0.15 is consistent with experiment. The effect of the Coulomb correlation between Co 3d electrons is also explored with the LSDA + U method. The Coulomb correlation at Co sites is not so large, $U \lesssim 1$ eV, and so CoS_2 is possibly categorized as an itinerant ferromagnet. It is found that the observed electronic and magnetic behaviors of CoS_2 can be described better by the LSDA than by the LSDA + U.Comment: 4 pages, 3 postscript figure

The Many Virtues of Second Nature : Habitus in Latin Medieval Philosophy

This chapter consists of a systematic introduction to the nature and function of habitus in Latin medieval philosophy. Over the course of this introduction, several topics are treated: the theoretical necessity to posit habitus; their nature; their causal contribution to the production of internal and external acts; how and why habitus can grow and decay; what makes their unity when they can have multiple objects and work in clusters. Finally we examine two specific questions: why intellectual habitus represent a special case that triggered considerable debate; how human beings can be said to be free if their actions are determined by moral habitus

Thermal behavior of covalently bonded phosphonate flame-retarded poly(methyl methacrylate) systems

Pyrolysis studies of reactively flame-retarded methyl methacrylate copolymers MMA/diethyl(acryloyloxymethyl)phosphonate (MMA/DEAMP) and MMA/diethyl(methacryloyloxymethyl)phosphonate (MMA/DEMMP) have been undertaken with a view to gaining information pertinent to the mechanisms of their flame-retardant behavior. The homopolymer with and without the additive diethylethylphosphonate was also investigated for comparison purposes. Each system contained 3.5 wt% of phosphorus. A range of techniques, namely TG with EGA, DSC, SEM, laser and microfurnace pyrolysis mass spectrometry, and isothermal pyrolysis-GC-MS, enabled the study to be carried out under a range of conditions. In the case of the additive system, the additive was evolved prior to the polymer decomposition. Little or no char residue remained at the end of the decomposition. Thus, the additive acted almost completely in the vapor phase. In the case of the MMA/DEMMP and MMA/DEAMP copolymers, substantial char residues were formed with 1.0 and 2.5 wt% phosphorus contents, respectively. This is evidence that predominantly condensed phase flame retardation occurs in these systems. SEM studies showed the chars from both copolymers to have flaky and smooth surfaces. Both copolymer samples showed slower decomposition rates compared to PMMA, the MMA/DEAMP being the slowest. Decomposition of MMA/DEMMP occurred mainly via end-chain scission with both MMA and DEMMP appearing concurrently, which would facilitate condensed-phase flame-retardant action. On the other hand, in the case of MMA/DEAMP, end-chain scission is to some extent is inhibited so that both end and the slower random-chain scission occur. As a result, the decomposition of the acrylate system was slower than that of the methacrylate copolymer. The former system yields more char which contains the higher percentage of phosphorus than does the methacrylate copolymer. Thus, MMA/DEAMP showed the greater condensed-phase flame-retardant action. This is consistent with the results of our previous flammability studies of these copolymers. The flame-retardant abilities of these two phosphonate copolymers are assessed with reference to previous studies of their equivalent phosphate copolymers. Copyright © 2008 John Wiley & Sons, Ltd

Electron energy loss and inelastic x-ray scattering cross sections from time-dependent density-functional perturbation theory

The Liouville-Lanczos approach to linear-response time-dependent density-functional theory is generalized so as to encompass electron energy loss and inelastic x-ray scattering spectroscopies in periodic solids. The computation of virtual orbitals and the manipulation of large matrices are avoided by adopting a representation of response orbitals borrowed from (time-independent) density functional perturbation theory and a suitable Lanczos recursion scheme. The latter allows the bulk of the numerical work to be performed at any given transferred momentum only once, for a whole extended frequency range. The numerical complexity of the method is thus greatly reduced, making the computation of the loss function over a wide frequency range at any given transferred momentum only slightly more expensive than a single standard ground-state calculation and opening the way to computations for systems of unprecedented size and complexity. Our method is validated on the paradigmatic examples of bulk silicon and aluminum, for which both experimental and theoretical results already exist in the literature