Medium-Range Structural Order in Amorphous Arsenic

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Medium-range order (MRO) is crucial in amorphous materials but poorly understood.
• Understanding MRO in amorphous elemental systems like arsenic (a-As) is essential.

Purpose of the Study:

• To elucidate the origin and nature of MRO in amorphous arsenic (a-As).
• To compare the structural characteristics of a-As with amorphous phosphorus (a-P).
• To investigate the pressure-dependent structural behavior of a-As and a-P.

Main Methods:

• Advanced atomistic simulations utilizing machine-learned potentials.
• Automated workflows for deriving machine-learned potentials.
• Comparison of simulated structure factor with experimental data for a-As.

Main Results:

• Simulations accurately reproduce the experimental structure factor of a-As, including the first sharp diffraction peak (FSDP).
• Amorphous arsenic exhibits a more uniform dihedral-angle distribution than amorphous phosphorus, consistent with a continuous random network.
• The FSDP in a-As is linked to void size and distribution within the amorphous network.

Conclusions:

• The study provides fundamental insights into MRO in amorphous arsenic.
• The findings highlight the utility of automated machine-learning for atomistic simulations.
• Amorphous arsenic's structure is best described as a 3-fold coordinated continuous random network.