Linear equations Binding energy 12 Dirac equations 12 Lead 10 Wave functions 10 Atoms 8 Boundary conditions 8 Theoretical study 8 Finite element method 6 Inner-shell ionization 6 L-shell ionization 6 Perturbation techniques 6 Problem solving 6 Reaction diffusion equations 6 Response model 6 Shells (structures) 6 Target electrons 6 Approximation theory 4 Binding sites 4 Dielectric formalism 4 Diffraction 4 Electromagnetic wave polarization 4 Electromagnetic waves 4 Electron energy loss spectroscopy 4 Energy dissipation 4 Energy loss 4 Energy regions 4 Error analysis 4 Experimental data 4 Finite elements 4