摘要:

Results are presented of computer simulation studies of some uranium oxide phases, using two contrasting methods to calculate defect parameters. The first is based on the Mott-Littleton approach, which assumes defects to be in infinite dilution in an otherwise perfect lattice, and the second allows finite defect concentrations to be modelled, using a supercell approach. Two groups of uranium oxide compounds are studied; firstly the mixed oxide reactor fuel (U,Pu)O2, where lattice and defect properties are obtained as a function of Pu concentration, and secondly the alkaline earth metal uranates M3UO6, where the calculation of a complete set of structural data and defect parameters is described, and the dominant mode of intrinsic disorder proposed.

ISSN:1042-0150    

DOI:10.1080/10420159508227205

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Classical shell-model- as well as embedded-cluster-type calculations are employed in order to supply theoretical arguments in favour of hole bipolarons in BaTiO3. In particular the embedded cluster modelling studies, which explicitly include the local electronic defect structure, suggest the importance of lattice relaxation and electron correlation terms in order to stabilize diamagnetic O22−molecules (bipolarons) in the material. Our simulations show that hole bipolarons are predominantly bound at Ti-site acceptor defects.

ISSN:1042-0150    

DOI:10.1080/10420159508227206

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The lowest-energy lattices of polypyrrole and polythiophene in their planar conformations derived by atomistic lattice simulation agree with the results of diffraction studies on undoped polythiophene. When doped, the structures become layer lattices, the dopant ions occupying intercalation sites. A defect-lattice method to investigate the migration of Cl−and BF−4gives energy barriers 0.5–2.3 eV. The stabilisation of single chains and lattices of helical polythiophene requires olefinic character in the inter-ring bond. The ‘interleaving’ of the strands of adjacent chains requires the dopant ions to occupy sites in the axial region of the helical cavity, along which their migration is expected to be rapid.

ISSN:1042-0150    

DOI:10.1080/10420159508227207

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The electronic structures of Co2+and Ni2+ions are obtained by the molecular orbital LCGTO-LSD method. Electrostatic matrix calculations are performed for d3and d8configurations. Theoretical optical data are discussed in function of the impurity site location in the crystal cell.

ISSN:1042-0150    

DOI:10.1080/10420159508227208

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The Si(001)/SiO2(tridymite) interface has been simulated using a Monte-Carlo method. It has been shown that in this way reasonable values of angles and interatomic distances are obtained. The oxygen defect formation energy dependence with different vacancy sites has been studied. Because of coulombic interactions, the formation of vacancies is much easier in the vicinity of the interface.

ISSN:1042-0150    

DOI:10.1080/10420159508227209

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The microscopic origin of the strong dependence displayed by the cubic field splitting parameter, 10Dq, on the metal-ligand distance in transition metal complexes is explored within a realistic molecular orbital framework. Taking as a guide the case of the CrF63−Ohcomplex it is shown that though the admixture of 2s(F−) orbitals in the antibonding eg *(∼ 3z2—r2;x2– y2) orbital is very small [(Neλs)2≅ 5%] it is the main responsible of the law 10Dq α R−nwith n close to five. By contrast the admixture of 2p(F−) orbitals though more important [(Neλp[sgrave])2≅ 16%] is shown to be no relevant as regards the R dependence of 10Dq. Thus this analysis demonstrates that the R dependence of 10Dq is ultimately related to that displayed by the isotropic superhypefine constant for Ohcomplexes with unpaired [sgrave]-electrons.

ISSN:1042-0150    

DOI:10.1080/10420159508227210

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1042-0150    

DOI:10.1080/10420159508227211

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this contribution, we report the preliminary results of a theoretical calculation of relevant thermodynamic magnitudes involved in the RbF+CaF2→ RbCaF3solid state reaction. We combine pairwise and quantum-mechanical simulations to determine the static equations of state for the three crystals involved in this heterogeneous reaction. Then, we compute the standard enthalpy and volume of the reaction (Δ H°, Δ V°) and the dependence of Δ H and Δ V with pressure. Finally, the influence of crystal polymorphism in these magnitudes is examined.

ISSN:1042-0150    

DOI:10.1080/10420159508227212

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Taking the NaCl crystal as a test example, we analyze the performance of the Electron Gas model of Gordon and Kim with ionic electron densities obtained from the localized quantum-mechanical descriptions of the ions embedded in a quantum crystal potential. We also rationalize the potential answers of rigid and relaxed interionic potentials in terms of the charge densities used in their derivation.

ISSN:1042-0150    

DOI:10.1080/10420159508227213

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

It is preliminary reported how the consideration of the topology of the electronic density of B1 and B2 phases of alkali halides, obtainedviaquantum mechanical simulation, makes it possible to connect the stability or metastability of the lattices with geometrical factors. The latter turn out to validate the classical ionic model and some of the most controversial critics posed against it over the years.

ISSN:1042-0150    

DOI:10.1080/10420159508227214

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor