ISSN:0005-9021    

DOI:10.1002/bbpc.199700024

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractThe simplicity of density functional methods and the increasing availability of computer‐processing power have enabled ab initio modelling techniques to be applied to very large systems. Our own code, AIMPRO, enables the relaxation of clusters as large as 800 atoms while still maintaining full self‐consistency and a realistic basis. Moreover, the use of pseudopotentials means that applications to Ge clusters are no more time consuming than those built of C. An important thrust of our work has been the computation of accurate vibrational modes of defects and this has caught the attention of several prominent experimental groups with the consequence that joint studies of rather complicated defects have been successfully made. We outline the procedures used and discuss applications that have been made to a wide variety of non‐metallic systems such as vacancy defects in diamond, interstitial centres in silicon and carbon‐related defects in III–V

ISSN:0005-9021    

DOI:10.1002/bbpc.199700025

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractAtomistic simulation calculations are used to predict the solution mechanisms and the defect cluster geometries of: M2+dopant cations in Y2O3, M3+dopant cations in CoO and M2+dopant cations in SrTiO3. The interatomic potential parameters were derived by simultaneously fitting the properties of a range of mixed cation materials. The results suggest that although both solution enthalpies and cluster binding energies do scale with ionic radius, the relationships can be quite complex, materials specific and will not necessarily exhibit simple minima when the radius of the host cation equals the dopant cation, as described in previous studies.

ISSN:0005-9021    

DOI:10.1002/bbpc.199700026

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractIn this work we discuss the application of tight‐binding molecular dynamics to the study of migration of intrinsic point defects in c‐Si. In particular, we investigate self‐diffusion and formation of vacancy clusters. Furthermore, by means of Hartree‐Fock calculations, we present a quantitative picture for the chemical bond in silicon when point defects are

ISSN:0005-9021    

DOI:10.1002/bbpc.199700027

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractFirst principles periodic Hartree‐Fock calculations of Li:MnO, LixMnO2and CaMnO3are reported from which direct evidence is presented to indicate that the valence state of Mn remains essentially d5throughout the series. The net spin moment on Mn, on the other hand, follows that convential change from ∼5μBto ∼3μBassociated with the valence states Mn(II), Mn(III),

ISSN:0005-9021    

DOI:10.1002/bbpc.199700028

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractSome recent simulations of localized vibrational modes associated with substitutional impurities in crystals are discussed. Most of the examples are for impurities in III–V semiconductors and alkali halides, cases for which improvements in measurement and sample preparation techniques have generated new exacting tests for theoretical models. The displacements of atoms in the modes are revealed by the fine structure from isotopes of both the impurity and the host crystal atoms. Available schemes for modelling these dynamical properties of defects are reviewe

ISSN:0005-9021    

DOI:10.1002/bbpc.199700029

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractWe present a theoretical investigation on diffusion of atomic and molecular hydrogen in crystalline as well as amorphous silicon dioxide by means of molecular dynamics simulations. We report a characterization of the migration process of atomic hydrogen in quartz and tridymite and we provide an atomistic description of the diffusion of both atomic and molecular hydrogen in silica.

ISSN:0005-9021    

DOI:10.1002/bbpc.199700030

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractMolecular dynamics simulations of the solute migration by a vacancy have been made for a Lennard‐Jones model of solid argon. The results have been used to analyse the heat of transport,Q*, for solutes with masses corresponding to those of the noble gases. The theory shows that there are three contributions toQ*, coming from the fluxes of the kinetic energy, potential energy and a virial of the forces. Trends in the kinetic and potential terms are found with increasing mass of the solute atoms which it seems would be shown by solute atoms more generally. The molecular dynamics calculation is in the centre of mass frame and we give the necessary transformations to the required lattice fram

ISSN:0005-9021    

DOI:10.1002/bbpc.199700031

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractUsing a numerical simulation method, the electrostatic properties of grain boundaries in titanate ceramics (SrTiO3and BaTiO3) are calculated by the combination of a defect chemistry model and the general potential equation. Based on these results and a simple three‐dimensional “brick‐wall‐model” of the ceramic microstructure, an equivalent network is developed for the ceramic body which consists of a great number ofR C‐branches. Using this network it is possible to calculate the frequency dependence of the complex impedance of the ceramic. The results of the impedance simulation can be compared to experimental results. This comparison yields information about the charge transport across and along the grain boundaries and about the influence of the temperature, the bulk dopant concentrations, and the donor‐ or acceptor‐like grain boundary interface states on the electrical properties of the grain boundaries. By using the simulation technique one gets additional information to interpret and understand the experimental results and to model the physical and electrical behaviour of the grain boundaries which mainly determine the electrical characteristics

ISSN:0005-9021    

DOI:10.1002/bbpc.199700032

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractFirst principles periodic Hartree‐Fock calculations are reported of the electronic and magnetic structures and hole states in the T (La2CuO4) phases of Sr2CuO2F2, Sr2CuO2F2.5and NaSrCuO2F2. Sr2CuO2F2is predicted to be a highly ionic antiferromagnetic charge transfer insulator with Cu in a d9((dx2–y2)1) configuration. Holes are predicted to be highly localised spin polarons which destroy the AF ordering at concentrations of 0.5 per formula u

ISSN:0005-9021    

DOI:10.1002/bbpc.199700033

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY