Molecular dynamics simulations are performed to investigate the chemical products of molecular ethylene-cluster beam deposition on diamond substrates at room temperature. The substrates are hydrogen-terminated diamond (111) surfaces of varying sizes. The computational approach is molecular dynamics simulations with two different methods for determining the forces on the atoms: an empirical reactive empirical bond-order hydrocarbon potential and an order-N nonorthogonal tight-binding method. The results of these two approaches to thin-film nucleation through ethylene-cluster beam deposition are compared and contrasted. The results are used to determine the similarities, differences, advantages, and limitations of these two approaches.