  Binary neutron star mergers are thought to be one of the dominant sites of
production for rapid neutron capture elements, including platinum and gold.
Since the discovery of the binary neutron star merger GW170817, and its
associated kilonova AT2017gfo, numerous works have attempted to determine the
composition of its outflowing material, but they have been hampered by the lack
of complete atomic data. Here, we demonstrate how inclusion of new atomic data
in synthetic spectra calculations can provide insights and constraints on the
production of the heaviest elements. We employ theoretical atomic data
(obtained using GRASP$^0$) for neutral, singly- and doubly-ionised platinum and
gold, to generate photospheric and simple nebular phase model spectra for
kilonova-like ejecta properties. We make predictions for the locations of
strong transitions, which could feasibly appear in the spectra of kilonovae
that are rich in these species. We identify low-lying electric quadrupole and
magnetic dipole transitions that may give rise to forbidden lines when the
ejecta becomes optically thin. The strongest lines lie beyond $8000\,\r{A}$,
motivating high quality near-infrared spectroscopic follow-up of kilonova
candidates. We compare our model spectra to the observed spectra of AT2017gfo,
and conclude that no platinum or gold signatures are prominent in the ejecta.
From our nebular phase modelling, we place tentative upper limits on the
platinum and gold mass of $\lesssim$ a few $10^{-3}\,\rm{M}_{\odot}$, and
$\lesssim 10^{-2}\,\rm{M}_{\odot}$, respectively. This work demonstrates how
new atomic data of heavy elements can be included in radiative transfer
calculations, and motivates future searches for elemental signatures.
