Quantum and classical molecular dynamics simulations are discussed, illustrating the applicability of computer-based modelling to a broad range of materials systems and phenomena. Case studies ...discussed include: quantum simulations of fission dynamics of charged atomic clusters and metallization of finite, small, alkali-halide crystals, classical molecular dynamics investigations of the consequences of interfacial adhesive interactions leading to the formation of intermetallic junctions, and the molecular mechanisms of capillary processes.
A method for the evaluation of the angular width of an electron beam generated by a nanoconstriction is proposed and demonstrated. The approach is based on analysis of a narrow-width electron flow, ...that quantizes into modes inside a confining constriction which is described in the adiabatic approximation, evolving into a freely propagating electronic state after exiting the constriction. The method that we developed allows us to find the parameters and the shape of the constriction that are optimal for generation of extremely narrow electron beams. In the case of a constriction characterized by a linear widening shape an asymptotically exact solution for the injection problem is found. That solution verifies semi-quantitative results related to the angular characteristics of the beam, and it opens the way for determination of the distribution function of the electrons in the beam. We have found the relationship between the angular distribution of the electron density in the beam and the quantum states of the electrons inside the constriction. Such narrow electron beams may be employed in investigations of electronic systems and in data manipulations in electronic and spintronic devices.
A magnetic-field-effect transistor is proposed that generates a spin-polarized current and exhibits a giant negative magnetoresitance. The device consists of a nonmagnetic conducting channel (wire or ...strip) wrapped, or sandwiched, by a grounded magnetic shell. The process underlying the operation of the device is the withdrawal of one of the spin components from the channel, and its dissipation through the grounded boundaries of the magnetic shell, resulting in a spin-polarized current in the nonmagnetic channel. The device may generate an almost fully spin-polarized current, and a giant negative magnetoresistance effect is predicted.
We propose a ``spin-guide'' source for generation of electric currents with a high degree of spin polarization, allowing long-distance transmission of the spin-polarization. In the spin-guide scheme ...proposed here, a non-magnetic conducting channel is wrapped by a magnetic shell which preferentially transmits electrons with a particular spin polarization. It is shown that this method is significantly more effective then the spin-filter-like scheme where the current flows perpendicular to the interface between a ferromagnetic metal to a non-magnetic conducting material. Under certain conditions a spin-guide may generate an almost perfectly spin-polarized current, even when the magnetic material used is not fully polarized. The spin-guide is predicted to allow the transport of spin polarization over long distances which may exceed significantly the spin-flip length in the channel. In addition, it readily permits detection and control of the spin-polarization of the current. The spin-guide may be employed for spin-flow manipulations in semiconductors used in spintronic devices.
Photoelectron (PES) spectra from aluminum cluster anions (from 12 to 15 atoms) at various temperature regimes, were studied using ab-initio molecular dynamics simulations and experimentally. The ...calculated PES spectra, obtained via shifting of the simulated electronic densities of states by the self-consistently determined values of the asymptotic exchange-correlation potential, agree well with the measured ones, allowing reliable structural assignments and theoretical estimation of the clusters' temperatures.
