Surface energy, stress and structure of well-relaxed amorphous silicon: A combination approach of ab initio and classical molecular dynamics

In this study, a combined method of a classical molecular dynamics calculation with the Tersoff potential and an ab initio calculation based on density functional theory has been performed. This combination method can provide quantitative evaluation of the surface energy and surface stress of well-relaxed amorphous silicon in addition to its structure. Using this method, a surface energy of 1.05 ± 0.14 J/m2 and a surface stress of 1.5 ± 1.2 N/m are obtained. This calculation also leads to a new discovery of the microscopic characteristic of a-Si surfaces, which is not revealed through the use of an empirical potential. It is shown that there are two types of threefold coordinated atoms at the surface region; one with p3-like bonding and the other with sp2-like bonding. In addition, the investigation indicates that the microstructures of these defects are different from those of a threefold coordinated atom observed in the bulk structure.