Network connectivity and extended Se chains in the atomic structure of glassy GeSe4

In order to contribute to the ongoing debate on the atomic structure of Se-rich GexSe1-x glasses, we have studied the structure of glassy GeSe4 by first-principles molecular dynamics. The Perdew-Burke-Ernzerhof generalized gradient approximation has been employed. The nearest-neighbor Se environment is found to be compatible with the coexistence of a network of GeSe4 tetrahedra and Se-n chains, thereby confirming previous Perdew-Wang results. When comparing PW and PBE results, changes are found in the Ge-Ge coordination environment and in the number of GeSe4 tetrahedra. In addition, very extended Se-n chains (n > 3, up to n = 12) are present (PBE case)