Account Screening Effects Research Articles

Screening from eg states and antiferromagnetic correlations in d(1,2,3) perovskites: A GW+EDMFT investigation

We perform a systematic {\it ab initio} study of the electronic structure of Sr(V,Mo,Mn)O$_3$ perovskites, using the parameter-free $GW$+EDMFT method. This approach self-consistently calculates effective interaction parameters, taking into account screening effects due to nonlocal charge fluctuations. Comparing the results of a 3-band ($t_{2g}$) description to those of a 5-band ($t_{2g}$+$e_g$) model, it is shown that the $e_g$ states have little effect on the low-energy properties and the plasmonic features for the first two compounds but play a more active role in SrMnO$_3$. In the case of SrMnO$_3$ paramagnetic $GW$+EDMFT yields a metallic low-temperature solution on the verge of a Mott transition, while antiferromagnetic $GW$+EDMFT produces an insulating solution with the correct gap size. We discuss the possible implications of this result for the nature of the insulating state above the N\'eel temperature, and the reliability of the $GW$+EDMFT scheme.

Equation of state for dense non-isothermal plasma

In this work the effective potentials taking into account screening effects at large distances and quantum-mechanical effects of diffraction at small distances were used as models of interaction between particles. Thermodynamic properties of dense non-ideal non-isothermal plasma were calculated using these potentials and obtained on their basis radial distribution functions (RDFs). The influence created by difference between temperatures of electrons and ions was also considered and found to be able to significantly influence the effects in such plasmas.

Temperature Effects on Dynamical Conductivity of Graphene Based Systems

We have investigated dynamical conductivity of graphene based systems; Single Layer Graphene (SLG), Bilayer Graphene (BLG) and Single Layer Gapped Graphene (SLGG), at zero and finite temperatures by taking into the account screening effects within the Random Phase Approximation (RPA). Rσq,ω and Rσq,ω show peaks that correspond to single particle excitations (SPE) and collective excitations (CE) respectively. In SLG, SPE positions are observed at ωħ≈0.5εf,εf∧1.5εf for q0.5kf,kf∧1.5kf respectively for all values of temperature. The peak height increases with increasing electron momentum and temperature. We noticed that for finite momentumq0.5kf∧kf, the peak height is maximum for T=0K and minimum for T=0.5Tf while that for T=Tf is intermediate. We also noticed that Rσq,ω peaks are blue shifted at high temperature for all graphene systems. In case of BLG, Landau undamped peak has been observed at T=0 for finite momentumq=0.3kf which becomes smooth at T=0.5Tf∧Tf. For q=0.8kf, Landau damped plasmon peaks have also been observed for all values of temperature. No major changes are observed in case of SLGG, with respect to SPE and CE peaks positions and heights specifically due to small change in band gap value incorporated here.

Inclusion of screening effects in the van der Waals corrected DFT simulation of adsorption processes on metal surfaces

The DFT/vdW-WF2 method, recently developed to include the van der Waals (vdW) interactions in density functional theory (DFT) using the maximally localized Wannier functions, is improved by taking into account screening effects and applied to the study of adsorption of rare gases and small molecules, H${}_{2}$, CH${}_{4}$, and H${}_{2}$O on the Cu(111) metal surface, and of H${}_{2}$ on Al(111), and Xe on Pb(111), which are all cases where screening effects are expected to be important. Screening is included in DFT/vdW-WF2 by following different recipes, also considering the single-layer approximation adopted to mimic a screened metal substrate. Comparison of the computed equilibrium binding energies and distances, and the ${C}_{3}$ coefficients characterizing the adparticle-surface van der Waals interactions, with available experimental and theoretical reference data show that the improvement with respect to the original unscreened approach is remarkable. The results are also compared with those obtained by other vdW-corrected DFT schemes.

Fano effect on dynamical conductivity for perpendicular polarization in double-wall carbon nanotubes

The dynamical conductivity of double-wall carbon nanotubes for perpendicularly polarized light to the tube axis is studied by taking into account screening effects, exciton effects and depolarization effects within an effective-mass theory. The exciton peak of the semiconducting inner tube has an asymmetric line shape due to the coupling with a continuum state of the outer tube, indicating the Fano effect. The Fano coupling strength can be tuned by varying the inter-wall distance.

Probing the Topological Exciton Condensate via Coulomb Drag

The onset of exciton condensation in a topological insulator thin film was recently predicted. We calculate the critical temperature for this transition, taking into account screening effects. Furthermore, we show that the proximity to this transition can be probed by measuring the Coulomb drag resistivity between the surfaces of the thin film as a function of temperature. This resistivity shows an upturn upon approaching the exciton-condensed state.

WHY SCREENING EFFECTS DO NOT INFLUENCE THE CASIMIR FORCE

The Lifshitz theory of dispersion forces leads to thermodynamic and experimental inconsistencies when the role of drifting charge carriers is included in the model of the dielectric response. Recently modified reflection coefficients were suggested that take into account screening effects and diffusion currents. We demonstrate that this theoretical approach leads to a violation of the third law of thermodynamics (Nernst's heat theorem) for a wide class of materials and is excluded by the data from two recent experiments. The physical reason for its failure is explained by the violation of thermal equilibrium, which is the fundamental applicability condition of the Lifshitz theory, in the presence of drift and diffusion currents.

FIXED SCALE TRANSFORMATION APPROACH FOR BORN MODEL OF FRACTURES

We use the Fixed Scale Transformation theoretical approach to study the problem of fractal growth in fractures generated by using the Born Model. In this case the application of the method is more complex because of the vectorial nature of the model considered. In particular, one needs a careful choice of the lattice path integral for the fracture evolution and the identification of the appropriate way to take effectively into account screening effects. The good agreement of our results with computer simulations shows the validity and flexibility of the FST method in the study of fractal patterns evolution.

Fixed scale transformation for fracture growth processes governed by vectorial fields

We use the Fixed Scale Transformation (FST) approach to study the problem of fractal growth in fracture patterns generated by using the Born Model. The application of the method to this model is very complex because of the vectorial nature of the system considered. In particular, the implementation of this scheme requires a careful choice of the fracture path and the identification of the appropriate way to take into account screening effects. The good agreements of our results with computer simulations shows the validity and flexibility of the FST method which represents a general theoretical approach for the study of fractal patterns evolution.