The stress distribution in Si(111)/Si3N4(0001) and Si(111)/a-Si3N4 nanopixels are studied using molecular dynamics simulations on parallel computers. Bulk Si is described by the Stillinger-Weber potential and Si3N4 is represented by a combination of two- and three-body interactions that include steric, charge transfer, polarizability and covalent forces. The charge transfer at the interface is extracted from self-consistent electronic structure calculations. The molecular dynamics simulations for Si(111)/a-Si3N4 nanopixels involve two pixel sizes: 25nm and 54 nm (the systems consist of 3.7 million and 10 million atoms, respectively). In both systems we find stress domains at the interface, which extend into the silicon substrate. The nature of the stress domains is discussed.