92 research outputs found
Topological insulator behavior of WS \u3c inf\u3e 2 monolayer with square-octagon ring structure
No full text© 2016 Author(s). We report electronic behavior of an allotrope of monolayer WS2 with a square octagon ring structure, refereed to as (so-WS2) within state-of-the-art density functional theory (DFT) calculations. The WS2 monolayer shows semi-metallic characteristics with Dirac-cone like features around Cyrillic capital letter GHE. Unlike p-orbital\u27s Dirac-cone in graphene, the Dirac-cone in the so-WS2 monolayer originates from the d-electrons of the W atom in the lattice. Most interestingly, the spin-orbit interaction associated with d-electrons induce a finite band-gap that results into the metal-semiconductor transition and topological insulator-like behavior in the so-WS2 monolayer. These characteristics suggest the so-WS2 monolayer to be a promising candidate for the next-generation electronic and spintronics devices
Analytical solution of Mori's equation with hyperbolic secant memory
No full textThe 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
No full textThe 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
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