Stimulus dependence of the collective vibration of atoms in an icosahedral cluster.doc
《Stimulus dependence of the collective vibration of atoms in an icosahedral cluster.doc》由会员分享,可在线阅读,更多相关《Stimulus dependence of the collective vibration of atoms in an icosahedral cluster.doc(9页珍藏版)》请在三一文库上搜索。
1、免费查阅精品论文Stimulus dependence of the collective vibration of atoms in an icosahedral clusterLiu H. H. 1,Jiang E. Y. 1*,Bai H. L. 1,Wu P. 1,Li Z. Q1,Sun Chang Qing 21 Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology,Institute of Advanced Materials Physics,Faculty of
2、Science,Tianjin University,Tianjin(300072)2 School of Electrical and electronic Engineering, Nanyang Technological University, Singapore(639798)E- mail:,ecqsunntu.edu.sgAbstractMolecular dynamical calculations of the thermal relaxation of a Lennard-Jones 147-atom cluster revealedthat the collective
3、vibration of the atoms in the cluster at the initial stage of relaxation upon perturbation of dislocation and that the stability of the collective vibration is affected by the strength and extent of the mechanical stimulus. A stronger or larger-scale stimulus will cause the vibration to decay faster
4、 compared to the vibration stimulated by a weaker or small-scale stimulus. Understanding may suggest a possible way on how the stimulus-introduced energy is transferred in the cluster: the collective vibration of atoms and its decay.Keywords:molecular dynamics,nanostructures,lattice dynamics1. Intro
5、ductionExcitation by means of structure relaxation and electronic oscillation is of great importance in understanding the process of phase transition and energy transfer in materials 1,2,3,4,5. Among all sorts of vibration modes in material structure, collective vibration, or say collective excitati
6、on, stands out itself by consistent movement of a collection of particles 6,7,8,9. Such collectively excited states were first discovered in nuclei 10,11, and predicted in the free electron gas in metals by Pines et al. 12,13, then confirmed experimentally by Kaplan et al. 14. Using molecular dynami
7、c simulation, Salian et al 15, investigated the collective excitations in an Ar13 cluster. They moved the twelve atoms on the surface radially away of the center atom by the same distance, causing the cluster expanding to its maximum. They found in the subsequent relaxing process that the cluster ga
8、ve radial uniform expansion and contraction, which is considered to be collective atomic vibration.In the present work, we introduce dislocation stimulus into the icodahedral cluster containing147-atom with Lennard-Jones (LJ147) potential to study the relaxing process. Different from that conducted
9、by Salian et al.15, we disturb a certain portion of the atoms randomly, the monopole collective atomic vibration is found to be followed by a decay of the vibration. Results show that stronger stimulus can accelerate the decaying of the collective vibration.2. MethodWe may divide the LJ147 cluster,
10、from the central atom as core-0 to surface, into shell-1, shell-2, shell-3 16 as shown in Fig. 1. In order to show the relationship between the atoms clearly, we mark the atoms by groups Fig. 1b: the atoms on the vertex are marked as shell no a, those at the edges are marked as shell nob, those on t
11、he facets are marked as shell noc. For example, atoms on the vertex of shell-3 are marked as 3a, atoms at the edges of shell-2 are marked as 2b. Because there is only one sort of atoms in shell-1, we mark them as 1a.We combined the molecular dynamic simulation with Verlet algorithm 17 in calculation
12、. The atoms are bonded through the Lennard-Jones potential- 9 -ijP(rij) = 4( / rij)12 ( / r)6 , (1)whereri j is the distance between atom i and j . , and the mass of a single atom m areused as the unit of energy, length and mass, respectively. Then the unit of temperature and time wouldbe / k Bandm
13、2 / , respectively, where kBis the Boltzmann constant. We can obtain thepositions and velocities of atoms each time by Verlet algorithm, the time interval between two timesteps is set to be104 m 2 / .At the beginning of the simulation, we introduced weak stimulus into specific local structures of th
14、e LJ147 cluster by moving randomly the specified atoms a short distance dxyz along axis x, y and z. Larger dxyz means heavier stimulus. For convenience, we call dxyz as the scale of stimulus. Since the icosahedral LJ147 cluster is the global optimized configuration for clusters of this size, introdu
15、cing stimulus will provide excessive energy to the cluster. In the current work, we study how the position and energy of the specific atoms change during the excessive energy is released from the structure.We move randomly the atoms in core-2 (atoms in core-0, shell-1 and shell-2) and core-3 (atoms
16、in core-0, shell-1, shell-2 and shell-3, or say the atoms of the whole cluster) by dxyz along the x, y and z axis, then the positions and energies of atoms in the LJ147 cluster are investigated during the excessive energy is released.3. ResultsFirst, we introduce stimulus into core-2 with dxyz amoun
17、t at 0.01, 0.02, 0.03 and 0.04,respectively, in unit. The distance Di between the ith atom and the cluster center, as well as the potentialiienergy E p and the kinetic energy Ek of each atom, is investigated during the excessive energy is released.The first2 106time steps of the relaxing process are
18、 recorded. To investigate the relaxing process indetail,wefocusedontheinitialstage( (1.9 106 2.0 106 time step).i1 1105timestep)andthefinalstageFig. 2 shows how the Ekchanges in the initial and final stages of the relaxation process, in whichthe scale of the stimulus dxyz is denoted. Fig. 2 shows th
19、at when the dxyz is small (dxyz = 0.01), theifluctuation of the Ekis weak. The fluctuation becomes stronger as the dxyz is increased (for instances,idxyz = 0.02, 0.03, and 0.04), indicating that the atoms will gain more energy from stronger stimulus during the structure relaxation. From Fig. 2, we c
20、an also see that at the initial stage of relaxation, Ek shows synchronous fluctuation. However, the synchronous status decays gradually as the relaxing process goes on, and which becomes faster when the dxyz increases. It can be seen from Fig. 2 that at the final stage ofirelaxation, when dxyz = 0.0
21、1, the fluctuation of the Ekcould not be noticed when the dxyz is larger.Distill exhibits weak synchronous behavior, whichFig. 3 shows the fluctuation ofDiduring the relaxation. It could be seen that the fluctuating curvesofinvolve into groups according to the division in Fig. 1, which are denoted i
22、n Fig. 3. At the initialstage of the relaxation, the coincident fluctuation indicates clearly the collective movement of all theDiatoms. It can be found in Fig. 3 that the synchronous fluctuation ofdecays to chaotic status graduallyas the relaxing process is going on, which becomes faster as dxyz in
23、creases, implying that the collective movement decays gradually during the relaxation, and the strength of the original stimulus will affect theregularity of the movement of the atoms.iiSince the potential energy E p of the atoms is related to their positions, the E p curves also involve into differ
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- Stimulus dependence of the collective vibration atoms in an icosahedral cluster
链接地址:https://www.31doc.com/p-3619063.html