Structural properties of liquid Ge2Se3: A first-principles study

Abstract

The structural properties of liquid Ge${}_{2}$Se${}_{3}$were investigated by first-principles molecular dynamics using the Becke-Lee-Yang-Parr scheme for the treatment of the exchange-correlation functional in density functional theory. Our data for the total neutron structure factor and the total pair-distribution function are in excellent agreement with the experimental results. The structure is made predominantly ($\ensuremath{\sim}$61%) from units comprising fourfold coordinated Ge atoms in the form of Ge-GeSe${}_{3}$ or Ge-Se${}_{4}$ motifs, but there is also a large variety of motifs in which Ge and Se are not fourfold and twofold coordinated, respectively. The miscoordinated atoms and homopolar bonds lead to a highly perturbed tetrahedral network, as reflected by diffusion coefficients that are larger than in the case of liquid GeSe${}_{2}$. The network does, nevertheless, exhibit intermediate range order which is associated with the Ge-Ge correlations and which manifests itself by a first sharp diffraction peak in the total neutron structure factor. The evolution of the properties of Ge${}_{x}$Se${}_{1\ensuremath{-}x}$ liquids (0 $\ensuremath{\le}x\ensuremath{\le}$ 1) with composition is discussed.