Diffusion Time-Scale Invariance, Markovization Processes and Memory Effects in Lennard-Jones Liquids

We report the results of calculation of diffusion coefficients for Lennard-Jones liquids, based on the idea of time-scale invariance of relaxation processes in liquids. The results were compared with the molecular dynamics data for Lennard-Jones system and a good agreement of our theory with these data over a wide range of densities and temperatures was obtained. By calculations of the non-Markovity parameter we have estimated numerically statistical memory effects of diffusion in detail.Comment: 10 pages, 3 figure

Current correlation functions of ideal fermi gas at finite temperature

Expressions for transverse and longitudinal current-current correlation functions of an ideal Fermi gas describing the current fluctuations induced in the electron system by external probe perpendicular and parallel to the propagation of electron wave, have been obtained at finite temperature. The results obtained for transverse and longitudinal functions are presented for different values of wavelength and frequency at different temperatures. The diamagnetic susceptibility as a function of temperature has also been obtained from transverse current correlation function as its long wavelength and static limit, which smoothly cross over from known quantum values to the classical limit with increase in temperature

Monolayer, Bilayer and Heterostructures of Green Phosphorene for Water Splitting and Photovoltaics

We report the results of density functional theory (DFT) based calculations on monolayer and bilayer green phosphorene and their heterostructures with MoSe2. Both monolayer and bilayer green phosphorene are direct band gap semiconductors and possess anisotropic carrier mobility as high as 10^{4} cm^{2}V^{-1}s^{-1}. In bilayers, pressure of about 9 GPa induces the semiconductor-metal transition. Moreover, the band gap depends strongly on the thickness of the films and the external electric field. By employing strain-engineering under suitable solution conditions, monolayer and AC-stacked bilayer green phosphorene offer the band edge alignments which can be used for water splitting. The upper limit of the power conversion efficiencies for monolayer, AB- and AC-stacked bilayer green phosphorene heterostructures with MoSe_{2} is calculated to be 18-21 %. Our results show the possibility of green phosphorene to be used as photocatalytic and photovoltaic material in the energy-related applications.Comment: 23 pages, 7 figures, 2 table

Dynamic correlations in a charged Bose gas

We evaluate the ground-state properties of a charged Bose gas at T=0 within the quantum version of the self-consistent field approximation of Singwi, Tosi, Land, and Sjölander. The dynamical nature of the local-field correction is retained to include dynamic correlation effects. The resulting static structure factor S(q) and the local-field factor G(q) exhibit properties not described by other mean-field theories

Dynamic correlations in symmetric electron-electron and electron-hole bilayers

The ground-state behavior of the symmetric electron-electron and electron-hole bilayers is studied by including dynamic correlation effects within the quantum version of Singwi, Tosi, Land, and Sjolander (qSTLS) theory. The static pair-correlation functions, the local-field correction factors, and the ground-state energy are calculated over a wide range of carrier density and layer spacing. The possibility of a phase transition into a density-modulated ground state is also investigated. Results for both the electron-electron and electron-hole bilayers are compared with those of recent diffusion Monte Carlo (DMC) simulation studies. We find that the qSTLS results differ markedly from those of the conventional STLS approach and compare in the overall more favorably with the DMC predictions. An important result is that the qSTLS theory signals a phase transition from the liquid to the coupled Wigner crystal ground state, in both the electron-electron and electron-hole bilayers, below a critical density and in the close proximity of layers (d <~ r_sa_0^*), in qualitative agreement with the findings of the DMC simulations.Comment: 13 pages, 11 figures, 2 table

Shear viscosity of liquid mixtures: Mass dependence

Expressions for zeroth, second, and fourth sum rules of transverse stress autocorrelation function of two component fluid have been derived. These sum rules and Mori's memory function formalism have been used to study shear viscosity of Ar-Kr and isotopic mixtures. It has been found that theoretical result is in good agreement with the computer simulation result for the Ar-Kr mixture. The mass dependence of shear viscosity for different mole fraction shows that deviation from ideal linear model comes even from mass difference in two species of fluid mixture. At higher mass ratio shear viscosity of mixture is not explained by any of the emperical model

Analytical solution of Mori's equation with hyperbolic secant memory

The equation of motion of the auto-correlation function has been solved analytically using a hyperbolic secant form of the memory function. The analytical result obtained for long-time expansion together with short-time expansion provides a good description over the whole time domain as judged by a comparison with the numerical solution of the Mori equation of motion. We also find that the time evolution of the auto-correlation function is determined by a single parameter tau which is related to frequency sum rules up to fourth order. The autocorrelation function has been found to show simple decaying or oscillatory behaviour depending on whether the parameter tau is greater than or less than some critical value. Similarities as well as differences in the time evolution of the auto-correlation have been discussed for exponential, hyperbolic secant and Gaussian approaches of the memory function

Realization of a hyperbolic secant memory function

The Mori integrodifferential equation of motion has played a key role in the study of transport and dynamical properties of classical dense fluids. We have derived a hyperbolic secant form of the memory function from the Mori equation of motion using a Markovian approximation and an ansatz for its higher-order memory function. The validity of the memory function has also been investigated