Competition between fcc and icosahedral short-range orders in pure and samarium-doped liquid aluminum from first principles

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Development of structural order in liquid aluminum upon rapid cooling is studied by ab initio molecular-dynamics simulations and the recently developed atomistic cluster alignment method. We show that there is a strong competition between icosahedral and fcc short-range orders (SROs) in the system. Although the liquid eventually crystallizes into fcc structure when $T$ \ensuremath{\leqslant} 800 K, the icosahedral short-range order (ISRO) is found to be much stronger than the fcc SRO in the liquid. Doping of Sm in Al liquid can hinder the fcc crystallization and enhance the ISRO.