An empirical interatomic potential is introduced, which gives a convenient and relatively accurate description of the structural properties and energetics of carbon, including elastic properties, phonons, polytypes, and defects and migration barriers in diamond and graphite. The potential is applied to study amorphous carbon formed in three different ways. Two resulting structures are similar to experimental a-C, but another more diamondlike form has essentially identical energy. The liquid is also found to have unexpected properties. © 1988 The American Physical Society.