Structure of liquid GeSe: A first principle study

We have investigated liquid GeSe by first-principle molecular dynamics simulations performed in the framework of density functional theory. Our partial structure factors are in good agreement with recent experimental data. In particular, we do not find any evidence of intermediate range order, as indicated by the absence of a first sharp diffraction peak for low magnitudes of the momentum transfer in the partial structure factors. Comparison between experimental and calculated partial pair correlation functions g(alpha beta)(r) yields a less satisfactory agreement, non-negligible differences being found particularly in the shape and peaks position of the g(GeGe)(r) and g(SeSe)(r) for short distances (< 4 Angstrom). The origin of these discrepancies are discussed in the light of recent experimental and theoretical findings on other GexSe1-x disordered systems. Analysis of the atomic configurations reveals that this liquid GeSe does not exhibit a regular network structure. A variety of bonding configurations are found and, in particular, the subunits GeSe3 and SeGe3 are frequently observed. A conspicuous amount of Ge atoms form homopolar bonds, thereby favoring the occurrence of Ge-Ge-Se-3 groups in which the Ge-Ge bonds have a very short lifetime (similar to 0.5 ps). However, neither these groups nor the GeSe3 and SeGe3 subunits are predominant and play the role of the GeSe4 tetrahedra in the liquids GeSe4 and GeSe2, where structural order extended well beyond the first shell of neighbors. The lack of a prevailing structural feature in liquid GeSe correlates well with the absence of intermediate range order. (C) 2000 American Institute of Physics. [S0021- 9606(00)50437-1].