Orbital-free density functional theory (OFDFT) is a promising route to large-scale first-principles simulations, but its application to second-row covalent systems remains limited by the inaccurate description of localized, highly inhomogeneous densities and by the lack of angular-momentum dependence in conventional local pseudopotentials. Here, we develop a unified tight-binding orbital-free density functional theory framework that incorporates both nonlocal kinetic energy and nonlocal pseudopotential energy terms within the same reference-density expansion. In this formulation, a frozen reference density constructed from scaled atomic densities captures the dominant localized atomic contributions, while the self-consistent density variation accounts for bonding and environment-dependent effects. Meanwhile, the nonlocal pseudopotential energy density functional restores the angular-momentum-dependent electron-ion interactions essential for describing directional bonding. Benchmarks on representative B- and C-based covalent systems show that the proposed framework accurately reproduces the equation-of-state properties, relative energetics, and electron-density distributions of diverse boron allotropes while retaining the linear-scaling behavior of OFDFT. For carbon allotropes, the method captures the main structural and bonding trends, with remaining deviations mainly associated with the near-core kinetic energy density of dense $s{p}^3$ phases. These results establish a viable unified OFDFT framework for large-scale simulations of covalent materials and highlight the accuracy of near-core kinetic energy as a key challenge for further methodological development.

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• Electronic structure
• Density functional theory development
• First-principles calculations