  In bulk and low-dimensional extended systems, the screening of excitations by
the electron cloud is a key feature governing spectroscopic properties. Widely
used computational approaches, especially in the framework of many-body
perturbation theory, such as the GW approximation and the resulting approximate
Bethe-Salpeter equation, are explicitly formulated in terms of the screened
Coulomb interaction. In the present work we explore the effect of screening in
absorption and electron energy loss spectroscopy, concentrating on the effect
of local distortions on the screening and elucidating the resulting changes in
the various spectra. Using the layered bulk oxide V$_2$O$_5$ as prototype
material, we show in which way local distortions affect the screening, and in
which way changes in the screening impact electron energy loss and absorption
spectra including excitons. We highlight cancellations that make many-body
effects in the spectra very robust with respect to structural modifications,
while the band structure undergoes significant changes and the nature of the
excitations may also be affected. This yields insight concerning the
structure-properties relations that are crucial for the use of V$_2$O$_5$ as
energy storage material, and more generally, that may be used to optimize the
analysis and the calculation of electronic spectra in complex materials.
