# PhD Defense: Non-adiabatic processes in the radiation damage of materials from first principles

Ions shooting through solids produce damage of different kinds depending on the kind of projectile, its velocity and the kind of material. This damage can be of great importance in several contexts:in the nuclear industry (nuclear fuels, materials for hosting nuclear waste, structural materials in reactor chambers), in the electronics industry (the smaller a device the more sensitive to cosmic rays, especially in the space and aeronautics industries), and in ion radiotherapy of cancer, to name the most prominent. In all of these contexts it is important to be able to understand, control and predict the amount and character of the damage undergone by the relevant materials under the expected radiation. There are active research lines in radiation damage in all these contexts, which consider the damage under varied approximations.

In classical molecular dynamics simulations of the damage, the quantum mechanical dynamic response of the host electrons is completely ignored. The ion (projectile)-energy loss to the host electrons, characterized as electronic stopping power (ESP), is the most dominant dissipative mechanism over most of the projectile velocities. The ESP is one of the primary ingredients that dictates the early stages of damage.

A multitude of approximate models have been developed and applied to this problem since the early years of quantum physics. Following the pioneering work of Fermi and Teller [1], Lindhard in 1954 [2] and Ritchie in 1959 [3], applied a linear response formalism to study the energy loss in simple metals. In 1976, Almbladh et al. [4], and from 1981 onward Echenique et al. [5] have used density functional theory (DFT) to calculate the nonlinear response of the electron gas to the perturbation produced by a swift ion. Ever since the problem has been extensively studied using various approaches [6]. We have applied real-time time-dependent density functional (RT-TDDFT) formalism [7] to compute the ESP in different materials [8, 9].

[1] E. Fermi and E. Teller, Phys. Rev. 72, 399 (1947). [2] J. Lindhard, Dan. Mat. Fys. Medd. 28 (1954). [3] R. H. Ritchie, Phys. Rev. 114, 644 (1959). [4] C. O. Almbladh, U. von Barth, Z. D. Popovic, and M. J. Stott, Phys. Rev. B 14, 2250 (1976). [5] P. Echenique, R. Nieminen, and R. Ritchie, Solid State Commun. 37, 779 (1981). [6] C. P. Race, D. R. Mason, M. W. Finnis, W. M. C. Foulkes, A. P. Horseld, and A. P. Sutton, Rep. Prog. Phys. 73, 116501 (2010). [7] R. Ullah, A. Garaizar, F. Corsetti, D. Sanchez-Portal,

J. Kohano, and E. Artacho, Comput. Phys. Commun.

(in preparation) (2018). [8] R. Ullah, F. Corsetti, D. Sanchez-Portal, and E. Artacho,

Phys. Rev. B 91, 125203 (2015). [9] R. Ullah, E. Artacho, and A. A. Correa, Phys. Rev. Lett.

(submitted) (2018).

**Supervisor**: E. Artacho