Density functional theory insights into the structural, mechanical, electronic, and optical properties of WSe₂ using the HSE06 functional

Understanding the relationship between structural stability and anisotropic response is essential for evaluating bulk tungsten diselenide (WSe₂) for optoelectronic applications. In this work, the structural, elastic, electronic, optical, and vibrational properties of hexagonal 2H-WSe₂ are systematically investigated using density functional theory with the HSE06 hybrid functional in CASTEP. The optimized equilibrium lattice parameters a and c are 3.251 and 12.462 Å, respectively. The calculated elastic constants satisfy the Born stability criteria, while the absence of imaginary phonon frequencies along the sampled dispersion paths supports dynamical stability. Bulk and shear moduli of 68.85 and 39.43 GPa, respectively, indicate moderate stiffness, with a universal elastic anisotropy index of 0.898. WSe₂ exhibits an indirect band gap of 0.929 eV, increasing to 0.972 eV upon including spin–orbit coupling. Orbital analysis identifies hybridized W-5d/Se-4p valence states and predominantly W-5d conduction states. Optical calculations reveal pronounced polarization dependence, with static electronic dielectric constants of 16.33 and 10.73 for in-plane and out-of-plane polarization, respectively. Strong absorption occurs at 6.6–11.4 eV, while energy-loss maxima appear at 18.95 and 19.40 eV. These results establish a theoretical basis for exploring polarization-sensitive WSe₂ optoelectronics, although quantitative optical predictions require explicit treatment of electron–hole interactions.