Observation of single transits in supercooled monatomic liquids.

A transit is the motion of a system from one many-particle potential energy valley to another. We report the observation of transits in molecular dynamics calculations of supercooled liquid argon and sodium. Each transit is a correlated simultaneous shift in the equilibrium positions of a small local group of particles, as revealed in the fluctuating graphs of the particle coordinates versus time. To the best of our knowledge, this is the first reported direct observation of transit motion in a monatomic liquid in thermal equilibrium. We found transits involving 2-11 particles, having mean shift in equilibrium position on the order of 0.4R(1) in argon and 0.25R(1) in sodium, where R1 is the nearest neighbor distance. The time it takes for a transit to occur is approximately one mean vibrational period, confirming that transits are fast.