  This paper presents a large-scale $ab$ $initio$ simulation study of amorphous
silicon hydride ($a$-Si$_{\text{1-x}}$H$_{\text{x}}$) with an emphasis on the
structure and properties of the material across a range of hydrogen
concentration by combining accelerated molecular dynamics (MD) simulations with
first-principles density-functional calculations. The accelerated MD scheme
relied on classical metadynamics, which enabled the development of 2600+
high-quality structural models of $a$-Si$_{\text{1-x}}$H$_{\text{x}}$, with
system sizes ranging from 150 to 6,000 atoms and hydrogen concentrations vary
from 6 to 20 at. %H. The resulting amorphous networks were found to be
completely free from any coordination defects and that they all exhibited a
pristine band-gap in their electronic spectrum. The microstructural properties
of hydrogen distributions were examined with great emphasis on the presence of
isolated and clustered environments of hydrogen atoms. The results were
compared with a suite of experimental data obtained from x-ray diffraction,
infrared spectroscopy, spectroscopic ellipsometry and nuclear magnetic
resonance studies.
