Papers by Keyword: Empirical Potential

Abstract: Micromechanical cleavage is one of the methods used for isolation of single-and few-layer graphene sheets from bulk graphite. On the surface of peeled graphite flakes, nanosteps of precisely multiple-layer thickness are often observed. The nanosteps are believed to be termination edge of graphene sheets and formed by tearing graphene sheets sandwiched in the mouth of a main cleavage crack during the peeling process. In the present work, we introduce a continuum model to examine the peeling process that involves multiple fractures: the main cleavage fracture at the microscale, delamination of a graphene sheet from bulk graphite at the nanoscale, and tearing fracture of graphene at the atomistic scale. We apply von Karman's plate theory to model the graphene layer, the elastic fracture mechanics for the microscale cleavage crack, and a cohesive zone model for the nanoscale interlayer delamination and for the lattice-scale tearing fracture as well. With a reliable empirical interlayer potential, we could reveal the characteristic length scales involved in the multiscale fracture process. We show that the graphene layer is locally stretched to fracture in mode-I when von Karman's finite deflection effect in a plate is invoked, although the loading by the sandwiching cleavage crack faces is nominally tearing in mode-III.

Abstract: Atomistic simulations are used to describe the ½<111> screw dislocation in tungsten. Two different embedded atom model (EAM) potentials and one bond-order potential (BOP) are compared. A new analytical approach for constructing asymmetrical screw dislocations is presented.

Abstract: We have addressed two issues concerning the relative stabilities of various orienta- tions of interstitial clusters in iron by making a comprehensive comparison between four recent empirical potentials. First, we have investigated the effect of finite temperature on the com- petition between clusters made of a few dumbbells oriented along h111i or h110i. We show by quasi-harmonic calculations that h111i clusters have much larger vibrational formation en- tropies and that they are therefore stabilized with respect to h110i clusters at high temperature. Second, we have compared the formation energies of loops with several hundred atoms with Burgers vector 1 2 h111i or h100i. The 1 2 h111i loops are found to be always more stable, but the energy differences with h100i loops depend strongly on the potential.