Optical Properties and Correlation Effects in NaxCoO2

We have calculated the optical spectra of Na$_{x}$CoO$_2$ for $x$=0.3, 0.5, and 0.7 within the LDA. We compare our results to available experimental data and show that the important features and trends are reproduced well, but there is a nearly uniform shift of peak positions and poor agreement in intensities. We show, through application of a simple model, that these differences can be attributed to overhybridization between Co and O orbitals and spin fluctuations which renormalize the bandwidth. Applying the LDA+U procedure shifts the optical peaks further from their experimental locations, indicating that this method of incorporating correlation effects is ill-suited for the case NaxCoO2

True Dielectric and Ideal Conductor in Theory of the Dielectric Function for Coulomb System

On the basis of the exact relations the general formula for the static dielectric permittivity e(q,0) for Coulomb system is found in the region of small wave vectors q. The obtained formuladescribes the dielectric function e(q,0) of the Coulomb system in both states in the "metallic" state and in the "dielectric" one. The parameter which determines possible states of the Coulomb system - from the "true" dielectric till the "ideal" conductor is found. The exact relation for the pair correlation function for two-component system of electrons and nuclei g_ei(r) is found for the arbitrary thermodynamic parameters.Comment: 5 pages, no figure

Application of the Lifshitz theory to poor conductors

The Lifshitz formula for the dispersive forces is generalized to the materials, which cannot be described with the local dielectric response. Principal nonlocality of poor conductors is related with the finite screening length of the penetrating field and the collisional relaxation; at low temperatures the role of collisions plays the Landau damping. The spatial dispersion makes the theory self consistent. Our predictions are compared with the recent experiment. It is demonstrated that at low temperatures the Casimir-Lifshitz entropy disappears as $T$ in the case of degenerate plasma and as $T^2$ for the nondegenerate one.Comment: Accepted for publication in PR

Біофізичному віснику – 20 років

Біофізичному віснику – 20 років

On the Ground State of Electron Gases at Negative Compressibility

Two- and three-dimensional electron gases with a uniform neutralizing background are studied at negative compressibility. Parametrized expressions for the dielectric function are used to access this strong-coupling regime, where the screened Coulomb potential becomes overall attractive for like charges. Closely examining these expressions reveals that the ground state with a periodic modulation of the charge density, albeit exponentially damped, replaces the homogeneous one at positive compressibility. The wavevector characterizing the new ground state depends on the density and is complex, having a positive imaginary part, as does the homogeneous ground state, and real part, as does the genuine charge density wave.Comment: 6 double-column pages, 2 figures. 2nd version is an extension of the 1st one, giving more detail

Characterization of zigzag patterns on the surface of bovine serum albumin films

Analysis of the patterns formed during the drying of biological fluids is employed for research and diagnosis in medicine and agriculture. Saline solutions of native proteins and DNA are characterized by zigzag patterns, which could be quantitatively described using the specific length of zigzags Lspecific. The aim of this study was to analyze a wide number of characteristics in order to identify those most sensitive to the effects of various physical and chemical factors on the protein structure. We examined the films prepared from salt solutions of bovine serum albumin (BSA) under varying conditions, viz.: a proportional change in the concentration of the components, substitution of NaCl with NaF and NaBr, temperature treatment, gamma irradiation, and addition of trivalent iron and biologically active flavin mononucleotide. The results revealed that the distribution of zigzag segment lengths was approximately lognormal, and the distribution of angles between the segments was approximately logistic. Two parameters appeared to be the most informative, viz. the average length of the segments, mainly depending on Cl– concentration, and the number of segments, depending on: Cl– concentration, concentration of the non-aggregated (but not necessarily unfragmented) protein, and the excess concentration of ions and low molecular weight compounds