  Based on the results of computational simulations, the research addresses a
broad range of electronic and optical properties which are typical for two most
stable compositions of the yttrium oxyhydride, Y4H10O and YHO. Emphasis was
placed on characteristics of thin films of different structural phases.
Macroscopic optical properties were deduced and analyzed within the
conventional scheme that utilizes the knowledge of refractive index,
absorption, transmittance and reflectance spectra. Our major goal was two-fold:
First, to provide modeling and description of optical spectra for various
single- and bi-phase oxyhydride compositions, and second, to conduct
comparative analysis that would be powerful enough to explain the features of
the experimentally measured transmittance spectra. In the context of nonlinear
optics, for the P-43m noncentrosymmetric cubic structure of Y4H10O we evaluated
a frequency profile of the second-order susceptibility ${\chi}^{(2)}(2\omega)$
and showed that the bulk Y4H10O may exhibit a rather considerable optical
nonlinearity.
