  A thorough understanding of the electronic structure is a necessary first
step for the design of nanoelectronics, chemical/bio-sensors, electrocatalysts,
and nanoplasmonics using graphene. As such, theoretical spectroscopic
techniques to describe collective excitations of graphene are of fundamental
importance. Starting from density functional theory (DFT), linear response time
dependent DFT in frequency-reciprocal space within the random phase
approximation (TDDFT-RPA) is used to describe the loss function
-Im{1/{\epsilon}(q,{\omega})} for isolated graphene. To ensure any spurious
interactions between layers are removed, both a radial cutoff of the Coulomb
kernel, and extra vacuum directly at the TDDFT-RPA level are employed. A
combination of both methods is found to provide a correct description of the
electron energy loss spectra of isolated graphene, at a significant reduction
in computational cost compared to standard methods.
