Search results for "electron density"

Ab InitioModeling of Metal Adhesion on Oxide Surfaces with Defects

2000

Our ab initio studies show that surface defects cause redistribution of the electron density which can increase substantially the binding energy of metal atoms to oxide surfaces. The results for electron $({F}_{s}^{0})$ and hole $({V}_{s}^{0})$ centers in the adhesion of Ag atoms (at 1:4 and 1:1 coverages) to a MgO(100) surface, combined with previous studies for charged defects, support earlier ideas of the mechanism of radiation-enhanced adhesion of nonreactive metals on oxide substrates. The results suggest that some optical control of adhesion energies is possible through charge transfer.

Comparative density-functional LCAO and plane-wave calculations ofLaMnO3surfaces

2005

We compare two approaches to the atomic, electronic, and magnetic structures of LaMnO3 bulk and the (001), (110) surfaces—hybrid B3PW with optimized LCAO basis set (CRYSTAL-2003 code) and GGA-PW91 with plane-wave basis set (VASP 4.6 code). Combining our calculations with those available in the literature, we demonstrate that combination of nonlocal exchange and correlation used in hybrid functionals allows to reproduce the experimental magnetic coupling constants Jab and Jc as well as the optical gap. Surface calculations performed by both methods using slab models show that the antiferromagnetic (AF) and ferromagnetic (FM) (001) surfaces have lower surface energies than the FM (110) surfac…

Site symmetry approach in the supercell model of carbon-doped ZnO bulk

2017

Abstract Carbon-doped zinc oxide is one of promising materials for technological applications due to its ferromagnetism observed at room temperature. When using the hybrid DFT-HF Hamiltonian based on the PBE0 exchange-correlation functional for large-scale calculations on defective ZnO:C single crystal, we have shown that application of supercell model for carbon impurity located at O site of wurtzite-structured ZnO bulk results in the dependence of calculated formation energy of the point defect (Eform) on the selected site symmetry of the substituted atom in the supercell. For a more symmetric C3v site usually used for simulation of defective ZnO structures, values of formation energy per…

Interstitial-oxygen-atom diffusion in MgO.

1996

configuration is the ~111! dumbbell centered at a regular oxygen site, whereas face-centered and cube-centered configurations are higher in energy by 1.45 eV and 3.57 eV, respectively. The~111! configuration isclose in energy to the ~110! configuration, which allows the dumbbell to rotate easily on a lattice site. In allthese four cases the interstitial oxygen atom attracts considerable additional electron density from its nearestregular O

The hydration shell of myoglobin.

1992

The space in the unit cell of a metmyoglobin crystal not occupied by myoglobin atoms was filled with water using Monte Carlo calculations. Independent calculations with different amounts of water have been performed. Structure factors were calculated using the water coordinates thus obtained and the known coordinates of the myoglobin atoms. A comparison with experimental structure factors showed that both the low and the high resolution regime could be well reproduced with 814 Monte Carlo water molecules per unit cell with a B-value of 50 A2. The Monte Carlo water molecules yield a smaller standard R-value (0.166) than using a homogeneous electron density for the simulation of the crystal w…

Simultaneous determination of carrier lifetime and electron density-of-states in P3HT:PCBM organic solar cells under illumination by impedance spectr…

2010

We report new insights into recombination kinetics in poly(3-hexylthiophene):methanofullerene (P3HT:PCBM) bulk heterojunction (BHJ) solar cells, based on simultaneous determination of the density of states (DOS), internal recombination resistance, and carrier lifetime, at different steady states, by impedance spectroscopy. A set of measurements at open circuit under illumination was performed aiming to better understand the limitations to the photovoltage, which in this class of solar cells remains far below the theoretical limit which is the difference between the LUMO level of PCBM and the HOMO of P3HT (∼1.1 eV). Recombination kinetics follows a bimolecular law, being the recombination ti…

Aromaticity in Pericyclic Transition State Structures? A Critical Rationalisation Based on the Topological Analysis of Electron Density

2016

The nature of the electron delocalisation pattern within a cyclic structure, i. e. the aromatic character, is examined for six-membered pseudocyclic transition state structures (TSs) involved in five representative examples of so-called pericyclic reactions. Results of the electron localisation function (ELF) and the quantum theory of atoms in molecules (QTAIM) analyses of the electron density evidence that in four of the cases, at least one pair of atoms are not bound at the TS configuration, thus precluding a possible cyclic conjugation. These findings make it possible to rule out the aromatic character of these TSs. High values of the synchronicity Sy index at the TSs contrast with the b…

The Mysticism of Pericyclic Reactions: A Contemporary Rationalisation of Organic Reactivity Based on Electron Density Analysis

2018

High-pressure optical absorption in InN: Electron density dependence in the wurtzite phase and reevaluation of the indirect band gap of rocksalt InN

2012

We report on high-pressure optical absorption measurements on InN epilayers with a range of free-electron concentrations (5×1017–1.6×1019 cm−3) to investigate the effect of free carriers on the pressure coefficient of the optical band gap of wurtzite InN. With increasing carrier concentration, we observe a decrease of the absolute value of the optical band gap pressure coefficient of wurtzite InN. An analysis of our data based on the k·p model allows us to obtain a pressure coefficient of 32 meV/GPa for the fundamental band gap of intrinsic wurtzite InN. Optical absorption measurements on a 5.7-μm-thick InN epilayer at pressures above the wurtzite-to-rocksalt transition have allowed us to o…

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(-).