Thanks a lot.
The temperature is 300K or so. Actually, I am trying to calculate the symetrical tilt () grain boundary energies of copper. These are CSL(coincidence site lattice) boundary, so it is much easy for setting a periodical boundary condition in the plane (z-x) of grain boundary. For adding a periodical boundary condition in the other direction (y), The sandwich like model is used. The input file and initial atom positions are included in the attached files. Notice that the stacking sequence in fcc metal along  direction is ABAB…which are assigned with different element type (1-4) in the data file.
When you analyze the dump file, you will find that
(1) atoms move systematicly near the boundary at the beginning (particularly when you viewing along x () direction), however, atoms away from grain boundary seem keep constant at that time. Therefore, I asked the question. I still have a little confusion. As you know, the moving directions of the atoms are set arbitrarily, so the atoms should all move arbitrarily except the force is very large. Am I right?
(I tried to persuade myself with following arguments. First, the atoms sitting away from grain boundary are periodically set, so the net force is very low and the velocity doesn’t change so much. But for the atoms near grain boundary, the net force is large and the atoms move much larger.)
(2) when the height of simulation box is low (~<1nm), the grain boundary will disapear after several thousands of steps. It means a single crystal wil be the result. Is it a common phenomenum? Or I made something wrong. By the way, it is also found in the simulation of twist grain boundary. As the box’s height increases, the grain boundary can be kept.
Thanks for your attention.
in.GB.txt (769 Bytes)
tilt.txt (105 KB)
tilt1.txt (349 KB)