Search results for "lattice [space-time]"
showing 10 items of 692 documents
Lattice Dynamics in Wurtzite Semiconductors: The Bond Charge Model of CdS
1999
An extension of the adiabatic bond charge model of Rustagi and Weber is used to study the lattice dynamic properties of wurtzite-type compounds. The model has been applied to the description of the phonon dispersion of CdS, which has been recently measured by neutron scattering. The agreement with the neutron data is excellent with a small set of physically meaningful parameters. The eigenvector admixture of the E2 modes, calculated at the G-point, agrees with the experimental values obtained through the isotopic mass dependence of the optical modes and ab initio calculations.
First principles simulations of F centers in cubic SrTiO 3
2005
Atomic and electronic structure of regular and O-deficient SrTiO3 have been studied. Several types of first principles atomistic simulations: Hartree-Fock method, Density Functional Theory, and hybrid HF-DFT functionals, have been applied to periodic models that consider supercells of different sizes (ranging between 40 and 240 atoms). We confirm the ionic character of the Sr-O bonds and the high covalency of the Ti-O2 substructure. For the stoichiometric cubic crystal; the lattice constant and bulk modulus correctly reproduce the experimental data whereas the band gap is only properly obtained by the B3PW functional. The relaxed geometry around the F center shows a large expansion of the t…
Photoluminescence from strained InAs monolayers in GaAs under pressure
1994
bulk GaAs. At pressures above the band crossover two emission bands are observed. These bands, characterized by having negative pressure coefBcients, are attributed to the type-I transition between conduction-band X „and heavy-hole states of the InAs monolayer and the type-II transition &om X states in GaAs to InAs heavy-hole states. The results are interpreted in terms of tight-binding band-structure calculations for the strained InAs-monolayer — bulk-GaAs system. I. INTRODUCTION Highly strained InAs jGaAs heterostructures have recently attracted interest due to their unusual electronic and optical properties. ~ 4 Epitaxial isomorphic growth of InAs on GaAs can be achieved only up to a sma…
The Peculiar Physical Properties of Nanosized Ferroics (Nanoferroics)
2013
This Chapter contains the experimental facts about size effects in nanoferroics. They include ferroelectric, ferroelastic, magnetic and multiferroic nanostructured materials. The main peculiar feature of nanoferroics is the geometric confinement originating from their surfaces and interfaces. This is in contrast to the ordinary bulk ferroics, where the sample surface plays a minor role. In particular, in nanoferroics, the surface generates the physical properties gradients in the normal (to the surface) direction. This fact yields strong size effects and spatial inhomogeneity of the nanoferroics properties, which should be taken into account to get their adequate physical description. We re…
Crack bifurcations in a strained lattice
1996
Dynamic crack propagation in a strained, granular, and brittle material is investigated by modeling the material as a lattice network of elastic beams. By tuning the strain and the ratio of axial to bending stiffness of the beams, a crack propagates either straight, or it branches, or it bifurcates. The crack tip velocity is calculated approximately for cracks that propagate straight. In a bifurcated crack the number of broken beams follows a scaling law. The shape of the branches is found to be the same as in recent experiments.
From Lattice Valued Theories to Lattice Valued Analysis
2015
We claim and justify that the future of a fuzzy logic is in the interconnection of various well-developed theories. We are focused on a lattice valued analysis that unifies the treatments of atomic elements, sets of atomic elements, functions between sets of atomic elements and their properties. We clarify the relationship between a fuzzy function and its ordinary core. We discuss the property of continuity of a fuzzy function in a lattice valued topology.
Fulde-Ferrell-Larkin-Ovchinnikov pairing in one-dimensional optical lattices
2008
Spin-polarized attractive Fermi gases in one-dimensional (1D) optical lattices are expected to be remarkably good candidates for the observation of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. We model these systems with an attractive Hubbard model with population imbalance. By means of the density-matrix renormalization-group method, we compute the pairing correlations as well as the static spin and charge structure factors in the whole range from weak to strong coupling. We demonstrate that pairing correlations exhibit quasi-long-range order and oscillations at the wave number expected from the FFLO theory. However, we also show by numerically computing the mixed spin-charge static …
Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms
2012
The transport measurements of an interacting fermionic quantum gas in an optical lattice provide a direct experimental realization of the Hubbard model—one of the central models for interacting electrons in solids—and give insights into the transport properties of many-body phases in condensed-matter physics.
Anomalous diffusion of polymers in supercooled melts near the glass transition
2007
Two coarse-grained models for polymer chains in dense melts near the glass transition are investigated: the bond fluctuation lattice model, where long bonds are energetically favored, is studied by dynamic Monte Carlo simulation, and an off-lattice bead-spring model with Lennard-Jones forces between the beads is treated by Molecular Dynamics. We compare the time-dependence of the mean square displacements of both models, and show that they become very similar on mesoscopic scales (i.e., displacements larger than a bond length). The slowing down of motions near the glass transition is discussed in terms of the mode coupling theory and other concepts.
Computer Simulations and Coarse-Grained Molecular Models Predicting the Equation of State of Polymer Solutions
2010
Monte Carlo and molecular dynamics simulations are, in principle, powerful tools for carrying out the basic task of statistical thermodynamics, namely the prediction of macroscopic properties of matter from suitable models of effective interactions between atoms and molecules. The state of the art of this approach is reviewed, with an emphasis on solutions of rather short polymer chains (such as alkanes) in various solvents. Several methods of constructing coarse-grained models of the simple bead–spring type will be mentioned, using input either from atomistic models (considering polybutadiene as an example) or from experiment. Also, the need to have corresponding coarse-grained models of t…