Role of electrons in collision cascades in solids. II. Molecular dynamics

Abstract

We present a model for the role of electrons in collision cascades in solids in which the coupling between ions and electrons is calculated using first-principles models and introduced into the classical ion equations of motion using our modified Langevin dynamics [Tamm et al. Phys. Rev. Lett. 120, 185501 (2018)]. This model gives a full picture of the entire collision process, from the ballistic to the thermal phases of a cascade, giving a detailed representation of the energy exchange between ions and electrons until their final thermalization, removing in this way some ad hoc assumptions used in the state-of-the-art two-temperature model. This work is separated into two papers; Part I [Caro et al. Phys. Rev. B (in press)] reports on the ab initio methodology used to translate stopping power into the parametrized dissipation function; this Part II applies the non-adiabatic ion dynamics using the dissipation functions developed in Part I to specific collision cascade events.

Integration of electronic effects into molecular dynamics simulations of collision cascades in silicon from first-principles calculations

“…This aspect is the most difficult and most important part of parametrizing the EPH model, and this article describes how to do it for Si in Section IV. The whole TDDFT calculations and the process of fitting to TDDFT were already performed on Ni and Ni alloys in [15] and [18].…”

“…The parameter that we really have to adjust, according to [15], is homogeneous to (eV.ps/ Å2 ), thus the square of α. It is sometimes called β in [15] and [18], has the same role in B IJ as α has in W IJ , as can be understood from (3) and ( 2), and can be seen as the electronic stopping power of the projectile divided by its velocity. The original papers of the EPH model [14,15,18] do not explicitly mention β in the equations although they actually name it in the text and optimize it.…”

“…As TDDFT has been shown to correctly describe the high energy electronic stopping power regime [16], but also electron-phonon processes occurring at very low energies (typically meV) [17], the EPH model therefore provides a framework for MD simulations accounting for electronic effects with very high accuracy. The model and its use on Ni and Ni alloys is described in [15] and [18].…”

Ab initio electronic stopping power for protons in Ga 0.5 In 0.5 P/GaAs/Ge triple-junction solar cells for space applications

“…The influence of the ESP on defect production by irradiation of different ions at different energies is under intense investigation [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Recent studies, which address the ESP problem from the ab initio point of view and combine it with the molecular dynamics simulations of damage cascades, show the importance of including electronic stopping effects in cascade formation, in terms of the number of formed defects and cascade morphology [22][23][24]. Electronic excitation, as a result of the moving primary and secondary projectiles in the first stages of the radiation damage process, can significantly alter the subsequent ionic displacements and the number of defects formed in the solid.…”

MeV irradiation of tungsten nanowires: structural modifications

“…Metallic nanowires have excellent electrical and thermal conductivity, but the size can dramatically affect these two properties. Recently, Tamm et al [63,64] have implemented a new version of the TTM-MD model in which they replace the scalar values of friction and random forces over individual particles with many-body forces that act in a correlated manner over different particles. This generalization allows modeling the electronic subsystem in a metal as a generalized Langevin bath equipped with a concept of locality due to correlation.…”