  Schwarzites are porous structures that present negative Gaussian curvatures.
Although initially proposed for carbon, in principle, schwarzites of other
elements are possible. In this work, we have carried out a detailed
investigation of the effect of element composition (C, Ge, Si, SiC, and BN) on
the structural, electronic and optical properties of a gyroid schwarzite
structure, the so-called G688. The DFT simulations were carried out using the
well-known SIESTA code. Our results showed that formation energy values are in
similar range of other related allotrope structures and are thermally stable
(up to 1000~K). From the electronic analyses, our results indicate that all
structures, except the carbon one, present semiconductor characteristics. From
the optical properties, except for the infrared region where only silicon and
germanium show some absorption, the other structures exhibit optical activity
only in the visible and ultra-violet regions, and all of them have large
refractive index values. For reflectivity, except for Si and Ge schwarzites
that reflect almost 40\% of light, the other schwarzites exhibit low
reflectivity. These characteristics make them good candidates for
optoelectronic applications, such as infrared/ultraviolet absorbers, and
ultraviolet blockers.
