  A simple method is proposed for inclusion of inelastic effects (electron
absorption) in computations of low-energy electron reflectivity (LEER) spectra.
The theoretical spectra are formulated by matching of electron wavefunctions
obtained from first-principles computations in a repeated vacuum-slab-vacuum
geometry. Inelastic effects are included by allowing these states to decay in
time in accordance with an imaginary term in the potential of the slab, and by
mixing of the slab states in accordance with the same type of distribution as
occurs in a free-electron model. LEER spectra are computed for various
two-dimensional materials, including free-standing multilayer graphene,
graphene on copper substrates, and hexagonal boron nitride (h-BN) on cobalt
substrates.
