  By molecular dynamics (MD) simulation of the one-component Dzugutov liquid in
a metastable equilibrium supercooled state approaching the glass transition, we
investigate the structural properties of highly mobile particles moving in
strings at low temperature T where string-like particle motion (SLM) is well
developed. We find that SLM occurs most frequently in the boundary regions
between clusters of icosahedrally-ordered particles and disordered,
liquid-like, domains. Further, we find that the onset T for significant SLM
coincides with the T at which clusters of icosahedrally-ordered particles begin
to appear in considerable amounts, which in turn coincides with the onset T for
non-Arrhenius dynamics. We find a unique structural environment for strings
that is different from the structure of the bulk liquid at any T. This unique
string environment persists from the melting T upon cooling to the lowest T
studied in the vicinity of the mode-coupling temperature, and is explained by
the existence of rigid elongated cages. We also form a criterion based solely
on structural features of the local environment that allow the identification
of particles with an increased propensity for mobility.
