Structural, optoelectronic, and magnetic properties of Q‑carbon studied by hybrid density functional theory ab initio calculations and experiment

Abstract

This work presents a theoretical study of the structural, optoelectronic, and magnetic properties of Q‑carbon, utilizing hybrid functionals within density functional theory (DFT) ab initio calculations. Moreover, experiments were conducted to measure structural parameters, dielectric functions, and magnetic properties, using various techniques. From the DFT simulations, structural, electronic, and optical properties have been simulated. The band gap energy was calculated using a hybrid approach, which combine HSE functional with different values of exact Hartree-Fock (HF) exchange (α). We propose a theoretical investigation of cubic and quasi-cubic forms of Q‑carbon. Our findings indicate that a non-cubic Q‑carbon cell is energetically more stable and possesses higher cell mass density and bulk modulus compared to a cubic cell. Calculations indicated that Q‑carbon exhibits semiconductor behavior; an indirect band gap of 3.10 eV and a direct band gap of about 3.4 eV was obtained for α = 0.44, in good agreement with experimental values. The density of states analysis allowed us to identify the p orbital of sp² hybridized atoms as being prevalent on the top of the valence band and in the lowest energy conduction band states. Magnetic moment values of 0.37 ${\mu }_B$ and 0.41${\mu }_B$ was found in two sp² bonded C atoms, in accordance with the experimental observation. Several optical properties were calculated. The theoretical findings are compatible with the experimental results shown here and available in the literature, with excellent agreement found between the calculated optical band gap and that obtained from absorption measurements.