  Amorphous silica (a-SiO$_2$) is a foundational disordered material for which
the thermal transport properties are important for various applications. To
accurately model the interatomic interactions in classical molecular dynamics
(MD) simulations of thermal transport in a-SiO$_2$, we herein develop an
accurate yet highly efficient machine-learned potential model that allowed us
to generate a-SiO$_2$ samples closely resembling experimentally produced ones.
Using the homogeneous nonequilibrium MD method and a proper quantum-statistical
correction to the classical MD results, quantitative agreement with experiments
is achieved for the thermal conductivities of bulk and 190 nm-thick a-SiO$_2$
films over a wide range of temperatures. To interrogate the thermal vibrations
at different temperatures, we calculated the current correlation functions
corresponding to the transverse acoustic (TA) and longitudinal acoustic (LA)
collective vibrations. The results reveal that below the Ioffe-Regel crossover
frequency, phonons as well-defined excitations, remain applicable in a-SiO$_2$
and play a predominant role at low temperatures, resulting in a
temperature-dependent increase in thermal conductivity. In the high-temperature
region, more phonons are excited, accompanied by a more intense liquid-like
diffusion event. We attribute the temperature-independent thermal conductivity
in the high-temperature range of a-SiO$_2$ to the collaborative involvement of
excited phonon scattering and liquid-like diffusion in heat conduction. These
findings provide physical insights into the thermal transport of a-SiO$_2$ and
are expected to be applied to a vast range of amorphous materials.
