To understand how these structures form and evolve, we simulated multi-layer, homoepitaxial growth on Al(110) and Ag(110) using ab initio kinetic Monte Carlo (KMC) simulations. In these simulations, we use the three-dimensional anisotropic bond-breaking model  to obtain the rates for atom diffusion. The energetic inputs to this model are obtained with first-principles, total-energy, density-functional theory calculations using VASP. At the high temperatures, where nano-huts form, the KMC simulations are slow because the diffusion of isolated adatoms is a very fast process. To tackle this problem, we developed a KMC method in which isolated adatoms are allowed to make multiple moves in one step. We achieve high efficiency with this algorithm and we are able to explore very high temperatures on large simulation lattices. We uncover a variety of interesting morphologies that depend on the growth temperature. In the low temperature regime we observe that, as the temperature increases, cross-channel <001> ripples, anisotropic mounds and in-channel <110> ripples form. These features are seen experimentally in studies of Ag(110) homoepitaxy . Various dormant processes in the low temperature regime are activated at higher temperatures to form nano-huts up to 50 monolayers high, with well defined and smooth (111) and (100) facets. Such huts are seen experimentally in Al(110) homoepitaxy .
By varying the interaction energies and the barriers for various rate processes, we have discerned the factors that determine the hut sizes and aspect ratios, as well as hut self-organization. The insight gained in this study could be employed to achieve selective nano-structure assembly in other growth scenarios.
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