Vacancy ordering and medium-range structure in a simple monatomic liquid

We analyze the origin of medium-range structural order in a simple monatomic liquid simulated by molecular dynamics. Convincing evidence is presented that this structural order, manifested by a prepeak in the structure factor, can be interpreted as chemical ordering in a mixture of atoms and atom-size vacancies. It is concluded that the liquid is able to sustain the presence of vacancies due to its predominantly icosahedral local order. The present result thus indicates that vacancy-induced medium-range order should be a common feature of icosahedrally ordered simple liquids, e.g., simple metallic glass formers.