  Understanding various macroscopic pressure-volume-temperature properties of
materials on the atomistic level has always been an ambition for physicists and
material scientists. Particularly, some materials such as zirconium tungstate
(ZrW2O8), exhibit multiple exotic properties including negative thermal
expansion (NTE) and pressure-induced amorphization (PIA). Here, using
machine-learning based deep potential, we trace both of the phenomena in ZrW2O8
back to a common atomistic origin, where the nonbridging O atoms play a
critical role. We demonstrate that the nonbridging O atoms confer great
flexibility to vibration of polyhedrons, and kinetically drive volume shrinking
on heating, or NTE. In addition, beyond a certain critical pressure, we find
that the migration of nonbridging O atoms leads to additional bond formation
that lowers the potential energy, suggesting that the PIA is a potential-driven
first-order phase transition. Most importantly, we identify a second critical
pressure beyond which the amorphous phase of ZrW2O8 undergoes a hidden phase
transition from a reversible phase to an irreversible one.
