First-principles molecular dynamics simulations are used to study the structural properties of liquid and crystalline ${\text{SnSe}}_2$. We reproduce the experimental structure factor with confidence and fully describe the pair-correlation functions and the local structure of the liquid. It is shown that, unlike other group IV chalcogenides such as ${\text{GeSe}}_2$, ${\text{SnSe}}_2$ does not display tetrahedral ordering in the liquid and contains a large amount of fivefold tin atoms with selenium atoms lying in an equatorial plane and at the edges of the polyhedra. A certain number of homopolar defects are found whose rate is substantially lower however than in ${\text{GeSe}}_2$. Compared to the crystalline system the density in the liquid decreases by 8.5%, which is accompanied by a decrease in the atomic coordination. Local distortions as found in typical phase-change materials are present in ${\text{SnSe}}_2$.

• Received 18 July 2008

DOI:https://doi.org/10.1103/PhysRevB.78.224209