A rigid-body-based multiple time scale molecular dynamics simulation of nanophase materials

Nanophase technology achieves superior material properties by assembling nanometer-size clusters. Structures on multiple-length scales and a hierarchy of time scales are essential for the design and control of nanophase materials. However, coexistence of a wide range of length and time scales hinders atomistic simulations of these materials. A new algorithm is developed for large-scale, longtime molecular dynamics simulations by combining (1) quaternion-based, rigid-body dynamics for global cluster motions; (2) implicit integration of Newton's equations for the coalescence of clusters; and (3) normal-mode analysis of fast atomic oscillations. The new scheme, using a time step Delta t of 10(-12) seconds, speeds up a Conventional explicit integration scheme (Delta t= 2 x 10(-15) seconds) by a factor of 28. A parallel implementation of the scheme achieves an efficiency of 0.94 for a 1.28-million-atom nanocrystalline silicon nitride solid on 64 nodes of an IBM SP computer.