Unveiling anisotropic and nonlinear electronic stopping in diamond under hydrogen irradiation: A real-time TDDFT study

Diamond's exceptional radiation tolerance makes it ideal for aerospace electronics, yet the atomistic mechanisms governing its electronic stopping power (Se) remain elusive. Using real-time time-dependent density functional theory (rt-TDDFT), we simulate hydrogen irradiation in bulk diamond along channeling (<100>, <110>, <111>) and off-channeling trajectories. Our results reveal striking anisotropy in Se, with the <110> channel showing 35% lower stopping power at the Bragg peak (v = 1.8 a.u.) than the <100>/<111> channels, correlated with reduced radial charge density. Off-channeling simulations further uncover nonlinear Se scaling at low velocities (v < 0.5 a.u.), defying free electron gas predictions. We attribute this to hydrogen-induced impurity states that facilitate bandgap bridging via Zener-like tunneling, enabling electron excitation even at ultralow velocities. Electronic structure analysis confirms orbital-selective contributions: 2p electrons dominate below v = 0.4 a.u., while deeper 2s electrons activate above v = 0.5 a.u., driving nonlinear energy loss. These insights establish diamond's unique electronic stopping behavior, critical for predicting radiation damage in extreme environments.