Lattice dynamics of calcium fluoride by an angular force model

The lattice dynamics of CaF₂ has been studied on the basis of a noncentral model using CGW type angular forces. The experimental data agree with the data obtained for the dispersion curves. The model has also been used to calculate lattice specific heat and Debye-Waller factors.     

A three-body force shell model calculation of Schottky defect formation energies of ionic crystals with CsCl structure

A three-body force shell model (TSM) for the calculation of Schottky defect formation energies in solids with cesium chloride structure has been developed by incorporating the effects of long-range three-body interactions (TBI) in the shell model. These TBI in the defect lattice arise from the deformation of electron shells when the nearest neighbour ions get relaxed from their equilibrium position. This model has been used to calculate the cation and anion extraction and Schottky defect formation energies of CsCl, CsBr, CsI, TlCl, TlBr and NH₄Cl crystals. The calculated values of these defect properties agree reasonably well with their measured values.     

Lattice dynamics of molecular solids by a phenomenological model

A quasiharmonic central-force rigid-atom model has been used to study the dispersion of phonon waves in molecular (rare-gas) solids. The model derives the interatomic forces by Buckingham-Corner potential and takes account of all neighbor interactions. Zero-point anharmonic effects have been taken into account through the potential parameters by a method of iteration. It is found that out of all the conventional power and exponential potentials the Buckingham-Corner potential function is best suited to this class of molecular solids. Further, the possibilities of the improvement of the present model have been discussed.     

Application of the three body force shell model to the lattice dynamics of calcium oxide

The lattice dynamics of GaO has been studied on the basis of the three body force shell model, which takes into account the effect of many body interactions in the lattice potential. The dispersion curves obtained by plottingω vsq agree fairly well with the experiments. It is concluded that the value of the molecular electronic polarizability of the solid must be must small than that determined experimentally which suggests that the interaction system in the solid may have a substantial covalent character.     

Structure of unstable nuclei in the sd-pf shell region by shell model with proper tensor force

Focusing on the importance of the tensor force in the effective interaction, we investigate the structure of unstable nuclei around N=28 with large-scale shell-model calculations. From the analysis of the spin-tensor decomposition for some interactions, the tensor force in the effective interaction should be close to the π+ ρ force, whereas it is much weaker in the Millener-Kurath (MK) interaction which is often used as the cross-shell interaction. The significance of the tensor force appears in the structure around ⁴²Si: the proper tensor force predicts that it is deformed contrary to the result from MK.     

Ab initio shell model calculations with three-body effective interactions for p-shell nuclei

We present a qualitative improvement of the ab initio no-core shell model (NCSM) approach by implementing three-body interaction capability for p-shell nuclei. We report the first calculations using three-body effective interactions derived from realistic nucleon-nucleon potentials for 6Li, 8Be, and 10B and demonstrate that the use of three-body effective interactions speeds up the convergence of the NCSM approach. For 10B, we predict JpiT = 1(+)0 ground state, contrary to the experimental observation of 3(+)0, when the AV8(') potential is used, indicating the need for true three-body forces.     

Lattice dynamics from vibronic spectra: Examination of a generalized shell model for SrF2 and BaF2

On the basis of quantum mechanical ab initio theories practical shell-models are established. These models include a polarization as well as a radial and axial deformation of the lattice ions, and are built up in such a way that measured macroscopic quantities can be incorporated. The predicted dynamics is tested by means of vibronic spectra of Sm²⁺ in SrF₂ and BaF₂. It turns out that both the structural form and the positions and intensities of the predominant vibronic maxima are very sensible to the high frequency dielectric constant ?_∞. An excellent agreement with the experimental result is found if ?_∞ fictitiously is chosen lower than the measured value, whereas the agreement would be considerably worse, if the experimental value itself of ?_∞ is choosen. Possible sources of these discrepancies are discussed.     

On the extended basis shell model and two-nucleon transfer

The enhancement of two-nucleon transfer reactions predicted by the extended basis shell-model (EBSM) calculations of Feng, Ibarra and Vallieres and other theorists, is shown to be a higher order manifestation of the pairing effects in nuclei. A simple schematic model is introduced which illustrates the constructive interference of the contributions from the highly excited shell-model states included in the EBSM. The model can be used to estimate the effect of ground-state correlations of the closed-shell core. The results indicate that the assumption of an inert core in EBSM calculations introduces negligible error in cases in which the addition of a nucleon pair to a closed shell is treated. However, in the case of two-nucleon removal from a closed shell, including the effects of correlations may significantly enhance the cross section. A suggestion is made for including these effects in EBSM calculations.     

Lattice dynamics of CuBr and CuI by a modified rigid ion model

Phonon dispersion relations of CuBr and CuI have been studied on the basis of a modified rigid ion model in which a non-central force system is used for the short-range interactions. The results of the calculations show a satisfactory agreement with the experimental data.     

The baryonic spectrum in a constituent quark model including a three-body force

We analyze, within a non-relativistic quark model, the low energy part of the baryonic spectrum in the octet and decuplet flavour representations. The relevance of a strong Coulomb potential is emphasized in order to explain its general features. The addition of a three-body force allows to solve the Roper puzzle, giving a consistent explanation to its relative position in the spectrum.This work has been supported by the grants CICYT: AEN-90-0040 and DGICYT: PB88-0064 and Acción Integrada HF-101. We are also grateful to V. Vento for illuminating discussions.     

三体核力重排项的同位旋效应

在同位旋相关的Brueckner理论框架内, 研究了三体核力重排贡献对同位旋对称势及其动量相关性和密度依赖性的影响，特别是研究了三体核力重排效应对于非对称核物质中质子和中子有效质量同位旋劈裂的影响. 结果表明: 三体核力重排效应对质子和中子单核子势均具有排斥性，而且其贡献随动量和密度增加而迅速增大. 在低密度区域，三体核力重排贡献对同位旋对称势的影响相当小，然而随着密度的升高，三体核力重排效应的贡献显著增强. 在高密度区域，三体核力重排效应使得同位旋对称势明显增大，而且当密度足够高时，三体核力重排贡献甚至导致对称势的动量相关性质发生改变. 三体核力的重排效应对核子有效质量同位旋依赖性的影响是使高密度丰中子核物质中质子-中子有效质量同位旋劈裂的幅度显著减小.     

Effect of three-body force on form factors

Conclusion The effect of increasing number of channels as well as the inclusion of the three-body force is very important in the charge form factor. We succeeded in getting a very good fit with the experimental result for³He. The experiment on³H is waited for. It will give important informations about the effect of the three-body force, as well as the neutron electro-magnetic form factor. A precise experiment about the first minimum of the magnetic form factor of³He is necessary.Presented at the symposium Mesons and light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

三体里德堡超级原子的关联动力学研究

因为寿命长,并且原子间相互作用容易操控,所以里德堡原子在量子信息与量子光学领域具有极大的吸引力.特别地,偶极阻塞效应成为执行很多量子信息处理任务的物理资源.本文基于严格的偶极阻塞效应,将捕获在三个磁光阱中的二能级里德堡原子系综看作超级原子,在此基础上研究原子数目可调控的三体里德堡超级原子的同相和反相动力学行为,同时实现W态和两种最大纠缠态的制备.本工作在量子操控和量子信息处理方面具有潜在的应用前景.     

The extended Hückel theory study of the self-trapped hole in CsF

The triatomic hole center [FCsF]⁰ observed in irradiated CsF crystal is studied by the method of the extended Hückel theory. The spin Hamiltonian parameters as well as the hole distribution on the three ions are determined. The results are in satisfactory agreement with experiment and indicate an inward relaxation of the pair of F^? ions.     

Lattice energy calculations for Ti4O7 using a shell model

The lattice energies of Ti₄O₇ containing Ti³⁺-Ti³⁺ pairs at temperatures below 120 K have been calculated by the polarizable point ion shell model. The positions of ions which minimize the total energy of the crystal have first been determined and then the lattice energies have been obtained using these ion positions. The defect energy is found to be 65.79 eV per eliminated oxygen ion. The ion positions determined in the calculation are, in general, found to move toward the positions in the real structure from their initial positions in the ideal structure. The lattice energies of the Ti₄O₇ structure in which the Ti³⁺ ions are redistributed hypothetically at the sites adjacent to the crystallographic shear planes have been also calculated. This was found to have a defect energy lower than the Ti₄O₇ structure with the distribution of valences observed experimentally. This result is discussed in terms of the quantum effect due to the nonmagnetic bond formed by electrons trapped on the Ti³⁺-Ti³⁺ pairs.     

Neutrino-12C scattering in the Ab initio shell model with a realistic three-body interaction

We investigate cross sections for neutrino-12C exclusive scattering and for muon capture on 12C using wave functions obtained in the ab initio no-core shell model. In our parameter-free calculations with basis spaces up to the 6 variant Planck's over 2pi Omega we show that realistic nucleon-nucleon interactions, like, e.g., the CD-Bonn, underpredict the experimental cross sections by more than a factor of 2. By including a realistic three-body interaction, Tucson-Melbourne TM'(99), the cross sections are enhanced significantly and a much better agreement with experiment is achieved. At the same time, the TM'(99) interaction improves the calculated level ordering in 12C. The comparison between the CD-Bonn and the three-body calculations provides strong confirmation for the need to include a realistic three-body interaction to account for the spin-orbit strength in p-shell nuclei.     

Application of three body force shell model to the lattice dynamics of transition metal oxides MnO,CoO and NiO

Lattice dynamics of some transition metal oxides has been studied using the three body force shell model. Reasonably good fits with the experimental phonon dispersion curves have been obtained by choosing values of molecular electronic polarisability substantially lower than those derived from the dielectric constant. This result is similar to those obtained in many other crystals which are not ideally ionic.     

Lattice dynamics of thorium

In the present work, a local model pseudopotential has been proposed to study the lattice dynamics of thorium. The model potential depends on the core and ionic radii, and accounts for the s-d-f hybridization effects in a phenomenological way. When this form of potential is applied to derive the phonon dispersion curves of Th, sufficiently good agreement is found between the computed and experimental results.