  We report on time-dependent density functional theory (TDDFT) calculations of
the excited states of 63 different graphene quantum dots (GQDs) in square shape
with side lengths 1 nm, 1.5 nm and 2 nm. We investigate the systematics and
trends in the UV-Vis absorption spectra of these GQDs, which are doped with
elements B, N, O, S and P at dopant percentages 1.5%, 3%, 5% and 7%. The
results show how the peaks in the UV and visible parts of the spectrum as well
as the total absorption evolve in the chemical parameter space along the
coordinates of size, dopant type and dopant percentage. The absorption spectra
calculated here can be used to obtain particular GQD mixture proportions that
would yield a desired absorption profile such as flat absorption across the
whole visible spectrum or one that is locally peaked around a chosen
wavelength.
