Description
Stopping power quantifies the energy transfer from an energetic particle (projectile) to a target material, which is generally expressed as the energy loss per distance travelled. For low-energy projectiles, nuclear stopping is the dominant contribution. This can be modelled using a binary collision model or molecular dynamics. For high-energy projectiles, excitation of electrons becomes the dominant energy loss mechanism. This is more challenging to model, and in nearly a century of research, numerous theoretical models and numerical approaches have been proposed. A key approximation built into analytical models and many numerical approaches is the assumption of a homogeneous target material. Additionally, as is the case with programs such as SRIM, stopping power predictions at low energies are limited to empirically derived corrections to approximate theoretical understanding. Recent advances in computing power and in electronic structure calculation methods now make it possible to simulate electronic stopping power from first-principles using time-dependent density functional theory (TDDFT). In practice, however, rapidly oscillating wavefunctions of tightly-bound core electrons makes all-electron simulations computationally prohibitive,
necessitating the use of a pseudisation scheme. Among these, the projector augmented-wave (PAW) method, originally formulated by Blochl [1], is widely adopted in density functional theory codes for its ability to approach all-electron accuracy [2]. In this work, the suitability of the PAW method for calculating electronic stopping power
with TDDFT is evaluated. To this end, a systematic approach for generating and selecting PAW datasets for both the target material and the projectile is developed, with an emphasis on transferability beyond the specific systems considered here. Finally, this framework is applied to an investigation of channelling effects in FCC aluminium, highlighting the importance of crystal structure on charged-particle transport.
[1] Blochl PE. Projector augmented-wave method. Physical Review B. 1994 Dec;50(24):17953-79. Available from: https://link.aps.org/doi/10.1103/PhysRevB.50.17953.
[2] Lejaeghere K, Bihlmayer G, Bj¨orkman T, Blaha P, Bl¨ugel S, Blum V, et al. Reproducibility in density functional theory calculations of solids. Science. 2016 Mar;351(6280):aad3000. Available from: https://www.science.org/doi/10.1126/science.aad3000.