Edwin Quashie edited section_Computational_and_Theoretical_Details__.tex  over 8 years ago

Commit id: 2b0d962389d8e0d91015b43a3e807f64e38771dc

deletions | additions      

       

\section{Computational and Theoretical Details}  In this work we employed the formalism of TDDFT coupled with Ehrenfest molecular dynamics (EMD)\cite{Gross_1996}\cite{Calvayrac_2000}\cite{Mason_2007}\cite{Alonso_2008}\cite{Andrade_2009} to simulate the collision processes between the target electrons and the ion (proton). In TDDFT-EMD, the dynamics of the electrons are treated quantum mechanically described by TDDFT and the nuclei are point particles treated classically using EMD. The strength of this method is used to calculate the electronic stopping power ($S_\text{e}$) for metals. We compared our results with those contained in \textsc{SRIM} database for the case of proton in $\mathrm{Cu}$.  The energy transfered to the electrons of the host atom ($\mathrm{Cu}$) from a constant velocity moving proton is carefully monitored. The energy loss of the proton is negligible hence total energy of the system is not conserved. This is because at the time scales of the simulations, the large mass of the proton guarantees a negligible decline in its velocity. As the proton moves, the time-dependent Kohn-Sham (TDKS) equation\cite{Runge_1984} describes electronic density and energy of the system due to the dynamics of effective single particle states under the external potential generated by the proton and the crystal of Cu nuclei. The TDKS equation can be written as (Hartree atomic units are used here):  \begin{equation}  \text{i}\frac{\partial}{\partial t}\Psi_{i}(\textbf r, t) = \left\{-\frac{1}{2}\nabla^{2} + V_{KS}[n](\textbf r, t)\right\}\Psi_i(\textbf r, t)