However, the influence of TBs on the mechanical behavior of metal nanospheres is still unclear up to now. This paper is to investigate the deformation mechanisms in twinned

copper nanoparticles subjected to uniaxial compression. Methods Consider a face-centered-cubic (fcc) copper nanosphere with parallel (111) coherent TBs under compression, as shown in Figure 1. The twin spacing is d and the loading direction varies #Cell Cycle inhibitor randurls[1|1|,|CHEM1|]# from [111] to indicated by a tilt angle θ between the twin plane and compressive plane. The embedded atom method (EAM) is utilized to describe the interactions between copper atoms [17], which has been widely adopted for copper crystals [18, 19]. Figure 1 Schematics of compression of twinned nanospheres. Simulation model (a) and internal twin structures (b). To simulate the compression process, a repulsive potential is employed to characterize the interaction between copper atoms and the planar indenter as [20, 21] (1) where

K is a specified force constant related to the hardness of indenter, h is the position of the compression plane, λ(z i – h) is the distance between the i-th atom and the planar indenter, H is the unit step function, and λ equals 1 for the top indenter, −1 for the bottom indenter, respectively. The molecular dynamics simulations are performed using LAMMPS developed by Sandia National Laboratories. In simulations, the surface of nanosphere is free, CYTH4 except atoms adjacent to the top and bottom indenters experiencing a repulsive potential. An NVT ensemble is chosen with Ilomastat order velocity-Verlet integration and a time step of 2.0 fs, and the temperature is controlled at

10 K using a Nosé-Hoover thermostat [22, 23]. Before compression, the systems are firstly equilibrated at 10 K for about 20 ps. During compression, the top and bottom indenters simultaneously move toward the center of the sphere with a constant velocity of approximately 10 m/s, and the compression depth δ is defined as the decreasing distance between the two indenters. We fix the radius of nanosphere as 15 nm and investigate the effects of TBs on the deformation of twinned nanoparticle. The total number of atoms in simulations is about 1.2 million. The common neighbor analysis (CNA) method is utilized to analyze the defect structures inside the deformed nanosphere [24]. In this method, atoms in perfect fcc lattice are distinguished from those in hcp lattice, surface, dislocation cores and other defects. Results and discussion Firstly, we examine the influence of twin spacing in nanosphere with the loading direction perpendicular to the TBs (θ = 0°). Figure 2 shows the load response of twinned nanospheres with twin spacing d varying from 1.25 to 5.09 nm. For comparison, the load response of a twin-free nanosphere is also included. Figure 2 Load versus compression depth response of nanosphere with different twin spacing.