Electronic, optical, and mechanical properties of novel h-C10N3 and h-C9N4 carbon nitride monolayers from first principles

ContextWe theoretically designed and systematically characterized two novel two-dimensional carbon nitride monolayers, h-C10$$_{10}$$N3$$_3$$ and h-C9$$_9$$N4, based on interconnected acepentalene motifs. Using density functional theory (DFT), we demonstrated their structural stability, confirmed by cohesive energies of -$$-$$6.89 eV/atom and -$$-$$6.92 eV/atom, respectively. Dynamical stability was validated by phonon calculations, revealing no significant imaginary frequencies, while ab initio molecular dynamics simulations showed thermal robustness at 300 K. Both monolayers exhibit metallic behavior, dominated by carbon and nitrogen pz$$p_z$$ orbitals near the Fermi level. Optical analysis revealed low reflectance and strong absorption peak at 2.2 eV for h-C9$$_{9}$$N4$$_4$$ and broad absorption within 1.8–3.1 eV for h-C10$$_{10}$$N3$$_3$$, suggesting potential as visible-light absorbers. Mechanical characterization indicated high elastic stiffness (Young’s modulus, 71-77 N/m), substantial shear resistance (23–25 N/m), and isotropic mechanical behavior (Poisson’s ratio, 0.55). Our findings position these new carbon nitride monolayers as promising candidates for flexible electronic devices, photodetection, and optoelectronic applications.MethodsFirst principles were performed using density functional theory (DFT) as implemented in VASP. The PBE functional with PAW pseudopotentials was employed, with a plane-wave cutoff of 520 eV. Thermal stability was assessed by ab initio molecular dynamics (AIMD) simulations at 300 K.