| Abstract: | Boundary conditions for molecular dynamics simulation of crystalline solids are
considered with the objective of eliminating the reflection of phonons. A variational formalism
is presented to construct boundary conditions that minimize total phonon reflection. Local
boundary conditions that involve a few neighbors of the boundary atoms and limited number
of time steps are found using the variational formalism. Their effects are studied and compared
with other boundary conditions such as truncated exact boundary conditions or by appending
border atoms where artificial damping forces are applied. In general it is found that, with the
same cost or complexity, the variational boundary conditions perform much better than the
truncated exact boundary conditions or by appending border atoms with empirical damping
profiles. Practical issues of implementation are discussed for real crystals. Application to
brittle fracture dynamics is illustrated. |
