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David C Langreth - One of the best experts on this subject based on the ideXlab platform.

  • van der waals density functional self consistent potential and the nature of the van der waals bond
    Physical Review B, 2007
    Co-Authors: Timo Thonhauser, Valentino R Cooper, Aaron Puzder, Per Hyldgaard, Shen Li, David C Langreth
    Abstract:

    We derive the exchange-correlation potential corresponding to the nonlocal van der Waals density functional [M. Dion, H. Rydberg, E. Schroder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004)]. We use this potential for a self-consistent calculation of the ground state properties of a number of van der Waals complexes as well as crystalline silicon. For the latter, where little or no van der Waals Interaction is expected, we find that the results are mostly determined by semilocal exchange and correlation as in standard generalized gradient approximations (GGA), with the fully nonlocal term giving little effect. On the other hand, our results for the van der Waals complexes show that the self-consistency has little effect on the Atomic Interaction energy and structure at equilibrium distances. This finding validates previous calculations with the same functional that treated the fully nonlocal term as a post-GGA perturbation. A comparison of our results with wave-function calculations demonstrates the usefulness of our approach. The exchange-correlation potential also allows us to calculate Hellmann-Feynman forces, hence providing the means for efficient geometry relaxations as well as unleashing the potential use of other standard techniques that depend on the self-consistent charge distribution. The nature of the van der Waals bond is discussed in terms of the self-consistent bonding charge.

Sadhan K Adhikari - One of the best experts on this subject based on the ideXlab platform.

  • fortran and c programs for the time dependent dipolar gross pitaevskii equation in an anisotropic trap
    Computer Physics Communications, 2015
    Co-Authors: Kishor R Kumar, Luis E Youngs, Dusan Vudragovic, Antun Balaž, P Muruganandam, Sadhan K Adhikari
    Abstract:

    Abstract Many of the static and dynamic properties of an Atomic Bose–Einstein condensate (BEC) are usually studied by solving the mean-field Gross–Pitaevskii (GP) equation, which is a nonlinear partial differential equation for short-range Atomic Interaction. More recently, BEC of atoms with long-range dipolar Atomic Interaction are used in theoretical and experimental studies. For dipolar Atomic Interaction, the GP equation is a partial integro-differential equation, requiring complex algorithm for its numerical solution. Here we present numerical algorithms for both stationary and non-stationary solutions of the full three-dimensional (3D) GP equation for a dipolar BEC, including the contact Interaction. We also consider the simplified one- (1D) and two-dimensional (2D) GP equations satisfied by cigar- and disk-shaped dipolar BECs. We employ the split-step Crank–Nicolson method with real- and imaginary-time propagations, respectively, for the numerical solution of the GP equation for dynamic and static properties of a dipolar BEC. The atoms are considered to be polarized along the z axis and we consider ten different cases, e.g., stationary and non-stationary solutions of the GP equation for a dipolar BEC in 1D (along x and z axes), 2D (in x – y and x – z planes), and 3D, and we provide working codes in Fortran 90/95 and C for these ten cases (twenty programs in all). We present numerical results for energy, chemical potential, root-mean-square sizes and density of the dipolar BECs and, where available, compare them with results of other authors and of variational and Thomas–Fermi approximations. Program summary Program title: (i) imag1dZ, (ii) imag1dX, (iii) imag2dXY, (iv) imag2dXZ, (v) imag3d, (vi) real1dZ, (vii) real1dX, (viii) real2dXY, (ix) real2dXZ, (x) real3d Catalogue identifier: AEWL_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEWL_v1_0.html Program obtainable from: CPC Program Library, Queens University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 111384 No. of bytes in distributed program, including test data, etc.: 604013 Distribution format: tar.gz

  • dynamics of quasi one dimensional bright and vortex solitons of a dipolar bose einstein condensate with repulsive Atomic Interaction
    Journal of Physics B, 2011
    Co-Authors: Luis E Youngs, P Muruganandam, Sadhan K Adhikari
    Abstract:

    By numerical and variational analysis of the three-dimensional Gross?Pitaevskii equation, we study the formation and dynamics of bright and vortex-bright solitons in a cigar-shaped dipolar Bose?Einstein condensate for large repulsive Atomic Interactions. A phase diagram showing the region of stability of the solitons is obtained. We also study the dynamics of breathing oscillation of the solitons as well as the collision dynamics of two solitons. At large velocities the frontal collision is elastic and the two three-dimensional solitons pass through each other undeformed. Two solitons placed side by side at rest coalesce to form a stable bound soliton molecule due to dipolar attraction. Movie clips illustrating collision and molecule-formation dynamics of two bright and vortex-bright solitons are included.

  • dynamics of quasi one dimensional bright and vortex solitons of a dipolar bose einstein condensate with repulsive Atomic Interaction
    arXiv: Quantum Gases, 2011
    Co-Authors: Luis E Youngs, P Muruganandam, Sadhan K Adhikari
    Abstract:

    By numerical and variational analysis of the three-dimensional Gross-Pitaevskii equation we study the formation and dynamics of bright and vortex-bright solitons in a cigar-shaped dipolar Bose-Einstein condensate for large repulsive Atomic Interactions. Phase diagram showing the region of stability of the solitons is obtained. We also study the dynamics of breathing oscillation of the solitons as well as the collision dynamics of two solitons at large velocities. Two solitons placed side-by-side at rest coalesce to form a stable bound soliton molecule due to dipolar attraction.

Xi Cheng - One of the best experts on this subject based on the ideXlab platform.

  • Atomically informed nonlocal semi discrete variational peierls nabarro model for planar core dislocations
    Scientific Reports, 2017
    Co-Authors: Guisen Liu, Xi Cheng, Jian Wang, Kaiguo Chen, Yao Shen
    Abstract:

    Prediction of Peierls stress associated with dislocation glide is of fundamental concern in understanding and designing the plasticity and mechanical properties of crystalline materials. Here, we develop a nonlocal semi-discrete variational Peierls-Nabarro (SVPN) model by incorporating the nonlocal Atomic Interactions into the semi-discrete variational Peierls framework. The nonlocal kernel is simplified by limiting the nonlocal Atomic Interaction in the nearest neighbor region, and the nonlocal coefficient is directly computed from the dislocation core structure. Our model is capable of accurately predicting the displacement profile, and the Peierls stress, of planar-extended core dislocations in face-centered cubic structures. Our model could be extended to study more complicated planar-extended core dislocations, such as {111} dislocations in Al-based and Ti-based intermetallic compounds.

  • Atomically informed nonlocal semidiscrete variational Peierls-Nabarro model for planar core dislocations
    DigitalCommons@University of Nebraska - Lincoln, 2017
    Co-Authors: Liu Guisen, Xi Cheng, Wang Jian, Chen Kaiguo, Shen Yao
    Abstract:

    Prediction of Peierls stress associated with dislocation glide is of fundamental concern in understanding and designing the plasticity and mechanical properties of crystalline materials. Here, we develop a nonlocal semi-discrete variational Peierls-Nabarro (SVPN) model by incorporating the nonlocal Atomic Interactions into the semi-discrete variational Peierls framework. The nonlocal kernel is simplified by limiting the nonlocal Atomic Interaction in the nearest neighbor region, and the nonlocal coefficient is directly computed from the dislocation core structure. Our model is capable of accurately predicting the displacement profile, and the Peierls stress, of planar-extended core dislocations in face-centered cubic structures. Our model could be extended to study more complicated planar-extended core dislocations, such as \u3c110\u3e {111} dislocations in Al-based and Ti-based intermetallic compounds

Wuming Liu - One of the best experts on this subject based on the ideXlab platform.

  • nonlinear dynamics of a bose einstein condensate excited by a vortex ring phase imprinting
    Results in physics, 2021
    Co-Authors: Wenkai Bai, Jianchong Xing, Tao Yang, Wenli Yang, Wuming Liu
    Abstract:

    Abstract We study the nonlinear dynamics of a three-dimensional Bose-Einstein condensate (BEC) excited by a vortex ring phase imprinting. We identify independent, integrated, and stationary modes of the center-of-mass oscillation of the condensate with respect to the vortex ring movement. We show that the oscillation amplitude of the center-of-mass of the condensate depends strongly on the initial radius of the vortex ring, the nonlinear inter-Atomic Interaction, and the aspect ratio of the trap, while the oscillation frequency is fixed and equals to the frequency of the harmonic trap in the direction of the ring movement. However, when applying Kelvin wave perturbations on the vortex ring, the center-of-mass oscillation of the BEC is changed non-trivially with respect to the perturbation modes, the long-scale perturbation strength as well as the wave number of the perturbations. The parity of the wave number of the Kelvin perturbations plays an important role on the mode of the center-of-mass oscillation of the condensate.

  • matter rogue wave in bose einstein condensates with attractive Atomic Interaction
    European Physical Journal D, 2011
    Co-Authors: Lin Wen, Sannian Song, Xiaofei Zhang, Wuming Liu
    Abstract:

    We investigate the matter rogue wave in Bose-Einstein condensates with attractive interAtomic Interaction analytically and numerically. Our results show that the formation of rogue wave is mainly due to the accumulation of energy and atoms toward to its central part; and the decay rate of atoms in unstable matter rogue wave can be effectively controlled by modulating the trapping frequency of external potential. The numerical simulation demonstrate that even a small periodic perturbation with small modulation frequency can induce the generation of a near-ideal matter rogue wave. We also give an experimental protocol to observe this phenomenon in Bose-Einstein condensates.

  • matter rogue wave in bose einstein condensates with attractive Atomic Interaction
    arXiv: Quantum Gases, 2011
    Co-Authors: Lin Wen, Sannian Song, Xiaofei Zhang, Wuming Liu
    Abstract:

    We investigate the matter rogue wave in Bose-Einstein Condensates with attractive interAtomic Interaction analytically and numerically. Our results show that the formation of rogue wave is mainly due to the accumulation of energy and atoms toward to its central part; Rogue wave is unstable and the decay rate of the Atomic number can be effectively controlled by modulating the trapping frequency of external potential. The numerical simulation demonstrate that even a small periodic perturbation with small modulation frequency can induce the generation of a near-ideal matter rogue wave. We also give an experimental protocol to observe this phenomenon in Bose-Einstein Condensates.

Gunther Schoeck - One of the best experts on this subject based on the ideXlab platform.

  • the emission of dislocations from crack tips a critical assessment
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003
    Co-Authors: Gunther Schoeck
    Abstract:

    Abstract The analytical treatment of dislocation emission at crack tips based on the Peierls concept is critically reviewed. Most treatments are based on the balance of stresses and must make a number of simplifying assumptions. Of special importance is to obtain the correct Atomic Interaction potential in the emission plane. In the literature, there exist some inconsistencies when combining the continuum concept of linear elastic fracture mechanics with the atomistic considerations of the Peierls model. It is also important to include the energy of ledge formation. Both aspects have a considerable influence on the critical stress intensity for dislocation emission and modify the γ us criterion of Rice. It is shown that these shortcomings can be overcome by treating dislocation emission as a variational problem of the crack energy.