Composition-tunable optoelectronic properties of gyroid schwarzites: a first-principles materials design study

Schwarzites are porous crystalline frameworks characterized by negative Gaussian curvature and three-dimensional periodicity. While originally proposed as carbon allotropes, recent advances in molecular preorganization and template-assisted synthesis concepts, together with the experimental realization of schwarzite-resembling molecular fragments, suggest that schwarzites may form a broader class of chemically tunable materials. In this work, density functional theory (DFT) calculations are employed to systematically investigate the structural, electronic, and optical properties of gyroid G688-schwarzites based on C, BN, SiC, Si, and Ge compositions. Cohesive energy analysis combined with ab initio molecular dynamics simulations demonstrates energetic and thermal stability of all investigated frameworks at room temperature, supporting their viability as metastable negatively curved crystalline phases. Electronic structure calculations reveal that all systems are semiconductors with composition-dependent direct bandgaps ranging from 0 to 2.87 eV, following trends analogous to those observed in their FCC counterparts. The optical response is strongly tunable across the ultraviolet and visible spectral regions, with distinct, element-dependent absorption, reflectivity, and refractive index profiles. These results establish chemical composition as an effective design parameter for tailoring the optoelectronic properties of negatively curved frameworks and provide first-principles guidance for future experimental efforts aimed at extending emerging bottom-up and template-based synthesis strategies beyond carbon-based schwarzites.