Short range order and network connectivity in amorphous AsTe₃: a first principles, machine learning, and XRD study

The atomic scale structure of amorphous AsTe₃ is investigated through X-ray diffraction, first-principles molecular dynamics (FPMD), and machine learning interatomic potentials (ML-GAP) obtained by exploiting the ab initio data. We obtain good agreement between the measured and modelled diffraction patterns. Our FPMD results show that As and Te obey the 8-N rule with average coordination numbers of 3 and 2, respectively. We find that small fractions of under and over coordinated As and Te atoms are present in the amorphous phase with about 6% (FPMD), and 13% (ML-GAP) of 3-fold Te. As is found at the center of pyramidal structures predominantly linked through Te_n chains rather than rings. Despite the low As concentration in AsTe₃, its local environment features a very high chemical disorder that manifests through the occurrence of homopolar bonds including at least 57% of As atoms.