These are freely-available parallel molecular dynamics codes, which may be well-suited to the problems you want to model. They can be used in conjunction with LAMMPS to perform complementary modeling tasks.
CHARMM, AMBER, GROMACS, NAMD, and Tinker are designed primarily for modeling biological systems. AMBER and CHARMM are the original classic codes in this genre. Gromacs, NAMD, and Tinker are more recently developed codes.
DL_POLY includes potentials for a variety of biological and non-biological materials. HOOMD is a very fast materials MD code designed to run on GPUs.
NWChem is both a molecular dynamics and quantum code which can model a variety of materials.