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1.
The structures of chromium-containing cluster centers in forsterite laser crystals Mg2SiO4 : Cr and Mg2SiO4 : Cr : Li have been simulated using the interatomic potential method. A system of position-dependent parameters of interatomic interaction potentials in forsterite has been developed. In the ionic approximation, this system adequately describes the structure, properties, and defects of the crystal with correct representation of the preferred positional arrangement of chromium ions. The preferred mechanisms of chromium dissolution in forsterite crystals have been evaluated from a comparison of the energies of formation of chromium-containing clusters with different configurations. It has been demonstrated that the results of the simulation of interatomic interaction potentials are consistent with the experimental data obtained from electron paramagnetic resonance and optical spectroscopy studies.  相似文献   

2.
H K Sahu  S Srinivasan  K Krishan 《Pramana》1980,15(2):189-205
Computer simulation studies have been made to investigate the static properties of mono-, di- and tri-vacancy clusters and of self-interstitials in hcp magnesium in different configurations. Three interatomic potentials have been chosen for which the results have been compared. A crystallite containing about 1500 atoms and a model with the interatomic interaction extending upto the fourth neighbour distance have been used. Relaxation field, defect relaxation and formation energies, strength dipole tensors and relative changes in volume in the above defects have been computed and our final results compared with those of earlier workers. The formation energies of the defects are highly sensitive to the choice of the potential whose detailed structure guides the nature of relaxation and the dipole tensors. Calculations have been done for octahedral, tetrahedral and dumb-bell interstitials of which the last is found to be the most stable.  相似文献   

3.
王天民  顾强  邢志强 《物理学报》1997,46(1):101-108
讨论了L12型合金中点缺陷的各种可能构型,然后运用分子动力学的方法,采用由Ack-land等提出的Cu-Au体系的多体势函数,计算了具有L12结构的Cu3Au与Au3Cu中点缺陷的构型、形成能及缺陷体积,并进一步讨论了目前研究较为深入的L12型金属间化合物中点缺陷的性质 关键词:  相似文献   

4.
The volume pinning force in superconductors with randomly distributed line defects nearly perpendicular to the flux lines is calculated for model as well as realistic interaction potentials between single defects and single flux lines. Both attractive and repulsive interactions defect — flux line were considered. The line defects were constructed from point defects distributed with constant density on straight lines. The deviations of the results from the theory of Labusch are considerable for small elementary interaction forces between defects and flux lines. The deviations (as well as the differences between repulsive and attractive interaction potentials) are larger for the realistic interaction potential than those for the different model potentials. The threshold values for the flux line distortion (under which no net volume pinning can exist) is also given.  相似文献   

5.
Thirty-nine unattributed electronic states of group IV monohalides have been interpreted in terms of Rydberg configurations. Ionization potential and quantum defects have been derived.  相似文献   

6.
In a two-dimensional (219) dusty plasma system, the size of particles is considered under two different interparticle potentials (Yukawa potential and Dressed potential). The structural and dynamical characters are investigated by molecular dynamics simulation respectively. The results show that the 2D systems via Yukawa and Dressed potentials have a different critical coupling constant F corresponding to the systems beginning to coagulate and exhibit different crystal configurations. Also we find that the size of particles has little influence on the 2D system's structure characters.  相似文献   

7.
We derive new duality relations that link the energy of configurations associated with a class of soft pair potentials to the corresponding energy of the dual (Fourier-transformed) potential. We apply them by showing how information about the classical ground states of short-ranged potentials can be used to draw new conclusions about the nature of the ground states of long-ranged potentials and vice versa. They also lead to bounds on the T=0 system energies in density intervals of phase coexistence, the identification of a one-dimensional system that exhibits an infinite number of "phase transitions," and a conjecture regarding the ground states of purely repulsive monotonic potentials.  相似文献   

8.
A general new technique to solve the two-center problem with arbitrarily oriented deformed realistic potentials is demonstrated, which is based on the powerful potential separable expansion method. As an example, molecular single-particle spectra for (12)C+(12)C-->(24)Mg are calculated using deformed Woods-Saxon potentials. These clearly show that nonaxial symmetric configurations play a crucial role in molecular resonances observed in reaction processes for this system at low energy.  相似文献   

9.
J. L. Bocquet 《哲学杂志》2013,93(22):3259-3295
Calculating the vibrational entropy of an N-atom assembly in the harmonic approximation requires the diagonalization of a large matrix. This operation becomes rapidly time consuming when increasing the dimensions of the simulation cell. In studies of point defects, a widely used shortcut consists in calculating the eigenmodes of the atoms contained in an inner region, called the defect region, while the atoms belonging to the outer region are held fixed, and in applying an elastic correction to account for the entropy stored in the distortion of the outer region. A recent paper proposed basing the correction on the local pressure change experienced by each lattice site. The present contribution is an extension in the sense that it includes shears. We compared the two approximations for configurations which are currently encountered in defect studies, i.e. defect formation and migration. The studied defects are the single, di- and trivacancy, as well as the dumbbell interstitial, in a host matrix modelled by several empirical potentials mimicking pure copper. The inclusion of shears adds a noticeable contribution to the elastic correction for all configurations of low symmetry.  相似文献   

10.
We apply the existence theorem for solutions of the equations of motion for infinite systems to study the time evolution of measures on the set of locally finite configurations of particles. The set of allowed initial configurations and the time evolution mappings are shown to be measurable. It is shown that infinite volume limit states of thermodynamic ensembles at low activity or for positive potentials are concentrated on the set of allowed initial configurations and are invariant under the time evolution. The total entropy per unit volume is shown to be constant in time for a large class of states, if the potential satisfies a stability condition.On leave from: Department of Mathematics, University of California, Berkeley, California.  相似文献   

11.
12.
Explicit expressions for one- and two-N1 isobar configurations in closed shell nuclei have been derived in the impulse approximation and applied to 4He and 16O. Conventional transition potentials with π- and ?-exchange have been used and the influence of potential regularization and short-range correlations have been studied. The dominant isobar configurations are found to be the one- and two-Δ components and originate from two-nucleon pairs in a relative S-state. The probability for finding a nucleon as a Δ-isobar is about 4.5% in 4He and about 3.2% in 16O. These numbers should be considered as upper limits due to uncertainties in off-shell effects of the transition potentials.  相似文献   

13.
An infinite system of Newton's equation of motion is considered for one-dimensional particles interacting by a finite-range hard-core potential of singularity like an inverse power of distance between the hard cores. Existence of limiting solutions is proved for initial configurations of finite specific energy and the semigroup of motion is constructed if energy fluctuations near infinity increase only as a small power of distance from the origin. In this case uniqueness of solutions is also proved and the solution is a weakly continuous function of initial data. The allowed set of initial configurations carries a wide class of probability measures including Gibbsian fields with different potentials. In the absence of hard cores limiting solutions are constructed for initial configurations with a logarithmic order of energy and density fluctuations.  相似文献   

14.
We demonstrate a novel method of introducing point defects (mono- and divacancies) in a confined monolayer colloidal crystal by manipulating individual particles with optical tweezers. Digital video microscopy is used to study defect dynamics in real space and time. We verify the numerical predictions that the stable configurations of the defects have reduced symmetry compared to the triangular lattice and discover that in addition they are characterized by distinct topological arrangements of the particles in the defect core. Surprisingly, point defects are thermally excited into separated dislocations, from which we extract the dislocation pair potential.  相似文献   

15.
《Physics letters. A》2014,378(30-31):2270-2274
We investigate electronic transport in the nitrogen-doped graphene containing different configurations of point defects: singly or doubly substituting N atoms and nitrogen–vacancy complexes. The results are numerically obtained using the quantum-mechanical Kubo–Greenwood formalism. Nitrogen substitutions in graphene lattice are modelled by the scattering potential adopted from the independent self-consistent ab initio calculations. Variety of quantitative and qualitative changes in the conductivity behaviour are revealed for both graphite- and pyridine-type N defects in graphene. For the most common graphite-like configurations in the N-doped graphene, we also consider cases of correlation and ordering of substitutional N atoms. The conductivity is found to be enhanced up to several times for correlated N dopants and tens times for ordered ones as compared to the cases of their random distributions. The presence of vacancies in the complex defects as well as ordering of N dopants suppresses the electron–hole asymmetry of the conductivity in graphene.  相似文献   

16.
The intermolecular potential energy surface for C3–He complex has been constructed using supermolecular CCSD(T) and MP4 methods. The potential surfaces have been calculated for 27 values of R ranging from 2.8 to 8.0 Å and 19 values of θ equally spaced between 0° and 180°. Both CCSD(T) and MP4 potentials have similar global behaviors. The global minimum in each of the potentials corresponds to the slightly distorted T-shaped geometry. On the basis of these two potentials, the intermolecular vibrational energies and wavefunctions were calculated. The energy level pattern of the vdW vibrational states was predicted for C3–He complex. The zero point bending motion of this complex has a range of 180°. The calculated fundamental frequency of vdW bending is 3.16 cm?1 at CCSD(T) level, and 5.38 cm?1 at the MP4 level. In addition, we have also constructed the intermolecular potential energy surface with C3 bending coordinate of 160° by using supermolecular CCSD(T) method. Two local minima including arrow-shaped and Y-shaped configurations were determined. The rotational constants of three C3–He structures including T-shaped, arrow-shaped and Y-shaped configurations at CCSD(T) level were also reported.  相似文献   

17.
The analytic embedded atom method (EAM) type many-body potentials of hcp rare earth metals (Dy, Er, Gd, Ho, Nd, Pr, and Tb) have been constructed. The hcp lattice is shown to be energetically most stable when compared with the fcc and bcc structure, and the hcp lattice with ideal c/a. The mechanical stability of the corresponding hcp lattice with respect to large change of density and c/a ratio is examined. The phonon spectra, stacking fault and surface energy are calculated. The activation energy for vacancy diffusion in these metals has been calculated and the most possible diffusion paths are predicted. Finally, the self-interstitial atom (SIA) formation energy and volume have been evaluated for eight possible sites. This calculation suggests that the crowdion and basal split are the most stable configurations. The SIA formation energy increases linearly with the increase of the melting temperature.Received: 26 March 2003, Published online: 9 September 2003PACS: 34.20.Cf Interatomic potentials and forces - 66.30.Fq Self-diffusion in metals, semimetals, and alloys - 61.72.Ji Point defects (vacancies, interstitials, color centers, etc.) and defect clusters - 61.72.Bb Theories and models of crystal defects  相似文献   

18.
We investigate confinement from new global defect structures in three spatial dimensions. The global defects arise in models described by a single real scalar field, governed by special scalar potentials. They appear as electrically, magnetically or dyonically charged structures. We show that they induce confinement, when they are solutions of effective QCD-like field theories in which the vacua are regarded as color dielectric media with an antiscreening property. As expected, in three spatial dimensions the monopole-like global defects generate the Coulomb potential as part of several confining potentials.Received: 25 August 2004, Published online: 16 March 2005PACS: 11.27. + d, 12.39.-x  相似文献   

19.
We consider equilibrium configurations ofn identical particles in three dimensions interacting via two-body potentials depending only on the distance. The symmetry group of a given configuration is defined as the subgroup of isometries which leaves it invariant, up to permutations of the particles. We prove the stability of the symmetry in the following sense: the symmetry group of an equilibrium configuration is the same for the neighboring equilibria arising from any small enough perturbation of the initial potential. Furthermore, for a large class of realistic potentials, the existence of nontrivial symmetries is proved, thus giving a completely geometrical, although partial, approach to the classical crystal problem.  相似文献   

20.
A frustration potential is a sum of interactions the terms of which are not simultaneously minimized even in the ground-state spin configurations. Ising models with such potentials can be discussed by the use of contours. The Peierls condition for the phase transition can be properly generalized, taking into account the presence of zero-energy contours. Frustration has some special features in two dimensions, which we study in detail. The connection with models of spin-glasses is discussed.  相似文献   

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