Although the present work is focused on the impact of coverage on normal modes, the vibrational partition function is not the only source of entropy for an adsorbate. The various possible configurations of adsorbates on a lattice also contribute to the overall entropy. In the case of ideal (non-interacting) adsorbates, the partial molar configurational entropy is given by the well-known formula s config = -k B ln θ 1-θ (see SI for a derivation) ]. An underlying assumption in this derivation is that all the combinatorial ways of arranging adsorbates result in the same energy. When lateral interactions are considered, however, this assumption is no longer applicable; the energy will vary-often considerably-with different arrangements. When the energies are not equal, the configurational partition function should be composed of both degeneracies and Boltzmann factors . The demanding task of linking the configurational degeneracy and the energetics makes accurate quantification of the configurational contribution challenging . Furthermore, the inhomogeneity of sites present even on simple metallic surfaces will bring in an additional layer of complexity. A more proper quantification of configurational entropy under non-ideal conditions will be the subject of forthcoming work. However, in the present study, we neglect the configurational contribution, but we acknowledge that it is certainly a crucial aspect to improve upon in the future.