Search results for "Density of state"
showing 10 items of 187 documents
A small spherical liquid: A DFT molecular dynamics study of WAu12
2009
The finite-temperature dynamics of WAu12, incorporating both electronic and structural effects, is studied using a density-functional-based Born-Oppenheimer molecular dynamics method. Molecular dynamics simulations for monomolecular WAu12 suggest a surface-melting-type behaviour of the angular degrees of freedom between 366 and 512 K. Thermally averaged electron density-of-states of WAu12 are compared to the experimental photoelectron spectra of WAu12(-).
Increased conductivity of a hole transport layer due to oxidation by a molecular nanomagnet
2008
Thin film transistors based on polyarylamine poly?N,N?-diphenyl-N,N ?bis?4-hexylphenyl?- ?1,1?biphenyl?-4,4?-diamine ?pTPD? were fabricated using spin coating in order to measure the mobility of pTPD upon oxidation. Partially oxidized pTPD with a molecular magnetic cluster showed an increase in mobility of over two orders of magnitude. A transition in the mobility of pTPD upon doping could also be observed by the presence of a maximum obtained for a given oxidant ratio and subsequent decrease for a higher ratio. Such result agrees well with a previously reported model based on the combined effect of dipolar broadening of the density of states and transport manifold filling. Peer Reviewed
First-principles calculations for SrTiO3() surface structure
2002
As a continuation of our recent abinitio calculations of SrTiO 3(1 0 0) surface relaxation for the two different terminations (SrO and TiO2) [Phys. Rev. B 64 (2001) 23417], we analyze here their electronic structures (band structure, density of states, and the electronic density redistribution with emphasis on the covalency effects). We compare results of abinitio Hartree–Fock method with electron correlation corrections and density functional theory with different exchange-correlation functionals, including hybrid (B3PW, B3LYP) exchange techniques. Our results are also compared with previous abinitio plane-wave local density approximation calculations and experiments when availab le. Consi…
Uncovering the metastable γ-Ag2WO4 phase: a joint experimental and theoretical study
2017
The synthesis of metastable solid phases is a pivotal starting point for innovative materials research. Here, we report the synthesis by means of a precipitation method of the metastable cubic γ-Ag2WO4 phase under ambient conditions. Different experimental techniques such as X-ray diffraction (XRD) with Rietveld refinement, field emission scanning electron microscopy (FE-SEM), micro-Raman/ultraviolet-visible (UV-vis) diffuse reflectance, photoluminescence spectroscopies, and differential scanning calorimetry (DSC) were employed. To complement the experimental data, the geometry, morphology, vibrational and electronic structure of γ-Ag2WO4 were characterized and evaluated using first-princip…
Defects, Disorder, and Strong Electron Correlations in Orbital Degenerate, Doped Mott Insulators.
2015
We elucidate the effects of defect disorder and $e$-$e$ interaction on the spectral density of the defect states emerging in the Mott-Hubbard gap of doped transition-metal oxides, such as Y$_{1-x}$Ca$_{x}$VO$_{3}$. A soft gap of kinetic origin develops in the defect band and survives defect disorder for $e$-$e$ interaction strengths comparable to the defect potential and hopping integral values above a doping dependent threshold, otherwise only a pseudogap persists. These two regimes naturally emerge in the statistical distribution of gaps among different defect realizations, which turns out to be of Weibull type. Its shape parameter $k$ determines the exponent of the power-law dependence o…
Coherent Control of Stimulated Emission inside one dimensional Photonic Crystals:Strong Coupling regime
2006
The present paper discusses the stimulated emission, in strong coupling regime, of an atom embedded inside a one dimensional (1D) Photonic Band Gap (PBG) cavity which is pumped by two counter-propagating laser beams. Quantum electrodynamics is applied to model the atom-field interaction, by considering the atom as a two level system, the e.m. field as a superposition of normal modes, the coupling in dipole approximation, and the equations of motion in Wigner-Weisskopf and rotating wave approximations. In addition, the Quasi Normal Mode (QNM) approach for an open cavity is adopted, interpreting the local density of states (LDOS) as the local density of probability to excite one QNM of the ca…
All-or-none proteinlike folding transition of a flexible homopolymer chain.
2009
Here we report a first-order all-or-none transition from an expanded coil to a compact crystallite for a flexible polymer chain. Wang-Landau sampling is used to construct the complete density of states for square-well chains up to length 256. Analysis within both the microcanonical and canonical ensembles shows a direct freezing transition for finite length chains with sufficiently short-range interactions. This type of transition is a distinctive feature of "one-step" protein folding and our findings demonstrate that a simple homopolymer model can exhibit protein-folding thermodynamics.
On the shell structure and geometry of monovalent metal clusters
1991
The Huckel model is used to study the electronic structure of monovalent metal clusters. In an fcc cluster the Huckel model gives an estimate to the electronic structure of a free electron cluster. It is shown that the surface faceting of the fcc cluster can destroy the electronic shell structure already when the cluster has about 100 electrons. In the Huckel model the icosahedral structure has smaller total energy than the fcc structures, from which the Wulff construction has the smallest energy already when the cluster has 600 atoms.
Ab initio calculations of the hydroxyl impurities in BaF2
2011
Abstract OH − impurities in BaF 2 crystal have been studied by using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW. Three different configurations of OH − impurities were investigated and the (1 1 1)-oriented OH − configuration is the most stable one. Our calculations show that OH − as an atomic group has a steady geometrical structure instead of electronic properties in different materials. The studies on band structures and density of states (DOS) of the OH − -impurity systems indicate that there are two defect levels induced by OH − impurities. The two superposed occupied OH − -bands located 1.95 eV above the valance bands (VB) at Γ point mainly consist…
First-principles simulations of H centers in CaF2
2014
Abstract H center, a hole trapped at an interstitial anion site, placed in the bulk and the (1 1 1) surface of calcium fluoride CaF2, has been studied by using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW. The H center orients the (1 1 1) direction for the bulk case and the (1 0 0) direction for the surface case, and the hole is mainly localized on the interstitial fluorine. The surface H center leads to a remarkable XY-translation of the surface atoms. Spin and hyperfine coupling calculations show a considerable interaction between the unpaired spin and the spin of neighboring nuclei, and the surface effect strengthens the spin polarization and hyperfine…