  A new connection between structure and dynamics in glass-forming liquids is
presented. We show how the origin of spatially localized excitations, as
defined by dynamical facilitation (DF) theory, can be understood from a
structure-based framework. This framework is constructed by associating
excitation events in DF theory to hopping events between energy minima in the
potential energy landscape (PEL). By reducing the PEL to an equal energy well
picture and applying a harmonic approximation, we develop a field theory to
describe elastic fluctuations about inherent states, which are energy
minimizing configurations of the PEL. We model an excitation as a shear
transformation zone (STZ) inducing a localized pure shear deformation onto an
inherent state. We connect STZs to T1 transition events that break the elastic
bonds holding the local structure of an inherent state. A formula for the
excitation energy barrier, denoted as $J_\sigma$, is obtained as a function of
inherent-state elastic moduli and radial distribution function. The energy
barrier from the current theory is compared to one predicted by the DF theory
where good agreement is found in various two-dimensional continuous
poly-disperse atomistic models of glass formers. These results strengthen the
role of structure and elasticity in driving glassy dynamics through the
creation and relaxation of localized excitations.
