A. Alkauskasa,b,S. Sagmeisterc, and C. Ambrosch-Draxlc, C. Héberta,b,
aEcole Polytechnique Fédérale de Lausanne (EPFL), Institute of Condensed Matter Physics, CH-1015 Lausanne, Switzerland
bEcole Polytechnique Fédérale de Lausanne (EPFL), Inderdisciplinary Centre for Electron Microscopy (CIME), CH-1015, Lausanne, Switzerland
cChair of Atomistic Modelling and Design of Materials, Montanuniversität Leoben, Franz-Josef-Strasse 18, A-8700 Leoben, Austria
It is generally assumed that random-phase-approximation (RPA) based on wavefunctions and the single-particle band structure from semilocal density functional theory calculations (such as the generalized gradient approximation, GGA) provides a sufficiently accurate description of the loss function for many materials. Si is a good example, in which GGA-RPA performs surprisingly well despite the “band-gap problem” inherent to the GGA. At variance, these calculations fail to provide the correct loss function of bulk Ag, in particular positions and the width of the main plasmon peak [1-3]. The main reason for this inadequate perfomance is that the 4d electronic states are predicted to be too close to the Fermi energy in semilocal approximations [1-4]. GGA-RPA yields the energy of the plasmon ~3.0 eV rather than the experimental ~3.8 eV, and, moreover, a substantially larger damping.
In the case of small momentum transfer and energy loss of <10 eV it has been shown that G0W0 or empirical  corrections to the band structure result in the much improved loss function. Notably, the position and the width of the main plasmon peak almost coincide with experimental values.
In the present work we study  the effect of G0W0 corrections on the momentum-dependent loss function with the exciting code. We analyze the dispersion of the plasmon and compare it to both available experimental data  and to GGA-RPA calculations . We also investigate the effect of G0W0corrections on the momentum-dependent loss function in the energy range 0-60 eV and for momentum transfers up to several reciprocal lattice vectors. Local-field effects are always included in our calculations. Many-body corrections yield the theoretical loss functions in a much better agreement with the experiment one  in the whole energy range.
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