Liquid boron and amorphous boron: An ab initio molecular dynamics study

The atomic structure of liquid and amorphous boron is investigated using an ab initio molecular dynamics technique. Liquid and amorphous states are found to have notably different microstructures and an average coordination number. Ideal and defective pentagonal pyramidal polyhedrons are the primary building unit of liquid boron but B12 icosahedra do not exist in the liquid state. During the rapid solidification, more ideal pentagonal pyramids develop progressively, resulting into a gradual formation of B12 icosahedra. On the basis of our findings, the atomic packing of pure amorphous boron is proposed to be somewhat close to that of the α-rhombohedral phase in contrast to the previous suggestions.