Search results for "ELECTRONIC STRUCTURE"

Ab initio electronic band structure calculation of InP in the wurtzite phase

2011

Abstract We present ab initio calculations of the InP band structure in the wurtzite phase and compare it with that of the zincblende phase. In both calculations, we use the full potential linearized augmented plane wave method as implemented in the WIEN2k code and the modified Becke-Johnson exchange potential, which provides an improved value of the bandgap. The structural optimization of the wurtizte InP gives a = 0.4150 nm , c = 0.6912 nm , and an internal parameter u = 0.371 , showing the existence of a spontaneous polarization along the growth axis. As compared to the ideal wurtzite structure (that with the lattice parameter derived from the zincblende structure calculations), the actu…

Theoretical investigation of the self-trapped hole in alkali halides. I. Long-range effects within the model hamiltonian approach

1994

A small-radius polaron model of the self-trapped hole (Vk-center) in alkali halide crystals is presented. Along with the usual contributions, the electronic polarization is also included in accordance with the electronic polaron theory of Toyozawa. It is shown that the exact solution of the problem within the Landau-Pekar approximation leads to multi-hole quantum states accompanied by the relevant electronic and lattice polarizations. As an example the KCl crystal is considered, for which the Vk-center structure as well as the self-trapping energy are computed. While solving our equations, the local symmetry of the defect is taken into account allowing us to consider a comparatively spread …

ChemInform Abstract: Magnetic and Electronic Structure of the CMR Chalcospinel Fe0.5Cu0.5Cr2S4

2010

Quantum chemical simulations of bound hold polarons (V Mg centers) in corundum crystals

1997

The semi-empirical INDO method has been applied to the calculations of the bound hole small-radius polarons in corundum. Results for optimized atomic and electronic structure using two different approaches (molecular cluster and periodic, supercell model) are critically compared. Both models find that two-site configurations of bound hole polarons have the lowest energy (which does not exclude existence of one-site polarons also characterized by essential relaxation energies). Experimental ENDOR data on V Mg defects are discussed in the light of the calculations.

Calculations of the atomic and electronic structure for SrTiO3 perovskite thin films

2001

The results of calculations of SrTiO3 (100) surface relaxation and rumpling with two different terminations (SrO and TiO2) are presented and discussed. We have used the ab initio Hartree–Fock (HF) method with electron correlation corrections and the density functional theory (DFT) with different exchange–correlation functionals, including hybrid exchange techniques. All methods agree well on surface energies and on atomic displacements, as well as on the considerable increase of covalency effects near the surface. More detailed experiments on surface rumpling and relaxation are necessary for further testing of theoretical predictions.

Lattice and electronic contributions to the refractive index of CuWO4

2014

We report an investigation of the refractive index dispersion and anisotropy in CuWO4 by means of interference measurements in two extinction directions from mid infrared to the visible region of the energy spectrum. The analysis of the refractive index dispersion yields ϵ(∞) = 4.5(1) for light polarization parallel to the c-axis and ϵ(∞) = 5.3(1) with respect to the other extinction axis. In addition, we report reflectance measurements carried out from the far infrared to the near ultraviolet to study the lattice and electronic contributions to the refractive index of CuWO4. We have determined the wavenumbers of nine infrared active lattice modes and compared them with previous ab initio c…

Quantum Monte Carlo study of insulating state in NaV2O5

2003

Abstract Quantum Monte Carlo (QMC) methods are being increasingly used as complements to Hartree–Fock (HF) methods for computing the electronic structure of molecules and materials. We investigate the nature of the insulating state driven by electronic correlations in the ladder compound NaV 2 O 5 ; considered as a quarter-filled system. We use an extended Hubbard model (EHM) to study the role of on-site and inter-site Coulomb interaction. It is found that the insulating state in the charge-disordered phase of this compound take origin from the transfer of spectral density and dynamical fluctuations. Our calculation allows us also, to understand the origin of the insulating states above T C…

DFT plane wave calculations of the atomic and electronic structure of LaMnO3(001) surface

2009

We present the results of ab initio DFT plane wave periodic structure calculations of the LaMnO3 (001) surface. The effects related to three different kinds of pseudopotentials, the slab thickness, magnetic ordering, and surface relaxation are studied and discussed. The antiferromagnetic surface lowest in energy (that is, the spins on Mn ions are parallel in basal plane and antiparallel from plane to plane) has a considerable atomic relaxation up to the fourth plane from the surface. The calculated (Bader) effective charges and the electronic density maps demonstrate a considerable reduction of the Mn atom ionicity on the surface accompanied by a covalent contribution to the Mn–O bonding.

Pressure Effect on Spin Crossover in [Fe(phen)2(NCS)2] and [CrI2(depe)2]

2004

In the present article, we discuss the results of investigations of the influence of hydrostatic pressure (up to 1.2 GPa) on the spin transition behavior in [Fe(phen)2(NCS)2] polymorph II and [CrI2(depe)2]. It is demonstrated that pressure effect studies are very helpful in elucidating the mechanism of cooperative dynamic electronic structure phenomena accompanied by significant volume changes. Application of hydrostatic pressure serves as a tool for modifying the ligand field strength in a controlled manner.

Intrinsic electrical conductivity of nanostructured metal-organic polymer chains

2012

One-dimensional conductive polymers are attractive materials because of their potential in flexible and transparent electronics. Despite years of research, on the macro- and nano-scale, structural disorder represents the major hurdle in achieving high conductivities. Here we report measurements of highly ordered metal-organic nanoribbons, whose intrinsic (defect-free) conductivity is found to be 104 S m−1, three orders of magnitude higher than that of our macroscopic crystals. This magnitude is preserved for distances as large as 300 nm. Above this length, the presence of structural defects (~ 0.5%) gives rise to an inter-fibre-mediated charge transport similar to that of macroscopic crysta…