We propose a unified mechanism to understand the remarkable stability of the body-centered cubic (bcc) phase in compressed solids, rooted in the orbital character of the electronic structure. In our previous study [Phys. Rev. B 108, 094112 (2023)], we showed that the contrasting high-pressure behavior of phosphorus (P), arsenic (As), and antimony (Sb)—where As and Sb adopt a stable bcc phase, but P does not—can be explained by whether a bonding-antibonding state composed purely of $p$ orbitals is preserved or not. In this paper, we extend this framework to the chalcogen elements and to the $d$-electron system titanium (Ti). First-principles calculations reveal that sulfur (S) exhibits a similar $p$-orbital-driven stabilization of the bcc phase, while heavier chalcogens are destabilized due to the occupation of antibonding $p$ states. In Ti, we identify a pressure-induced $s-d$ transition accompanied by the orbital-symmetry-resolved formation of a bonding-antibonding state within the $d$ manifold. Under high pressure, the electronic occupations of the $t_{2g}$ and $e_g$ orbitals approach an ideal 2:1 ratio, reinforcing the bonding framework and enhancing the stability of the bcc phase up to at least 1000 GPa. These results support a general criterion for the bcc phase stability in compressed elements based on orbital purity and symmetry, providing a unifying perspective across disparate chemical families.

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• Density of states
• Electronic structure
• High-pressure studies
• First-principles calculations