  Atom arrangement plays a critical role in determining material properties. It
is, therefore, essential for materials science and engineering to identify and
characterize distinct atom configurations. Currently, crystal structures can be
determined either by its static properties or by quantifying its structural
evolution. Here we show how to classify an atom into phase solely by its speed
dynamics. We model silicon crystals at different phase transition points and
use a single atom speed trajectory to demonstrate that
crystal-structure-independent Maxwell distribution of speed is generated by
crystal-structure-dependent atom dynamics. As the classification accuracy of
the method increases with trajectory length, we show that subtle difference in
local atomic structures can be identified using sufficiently long trajectories.
Thanks to symbolization of atom dynamics, the method is computationally
efficient and suitable for an analysis of large datasets on the fly.
