Accelerated molecular dynamics study of the GaAs(001)β2(2×4)/ c(2×8) surface

We develop an accelerated molecular dynamics method that has several advantages over conventional rare-event methods. We apply our method using a semiempirical Tersoff-Abell potential to understand the disordered structure of the GaAs(001)β2(2×4) surface at various temperatures. Our simulations indicate that the self-reconstruction of this surface is mediated by As-row-dimer and As-trench-dimer shifting events that typically occur over microsecond-millisecond times at temperatures of interest and that trench-dimer shifting occurs more rapidly than row-dimer shifting. Our calculations indicate that the equilibrium surface consists of an approximately equal mixture of β2(2×4) and c(2×8) domains, in agreement with an experimental scanning-tunneling microscopy study. Due to strain along the [11̄0] direction, there is a tendency for the surface to form long runs of in-phase As-row- and As-trench dimers. There are weak correlations between As-row-dimer pairs along the [110] direction such that the free energy of the c(2×8) surface is slightly lower than that of the β2(2×4) surface. This finding is also in agreement with the experiment and indicates the dynamical nature of this important substrate for thin-film growth.