Plane-wave density-functional theory calculations were performed using version 19.1 of the CASTEP code. The Brillouin zone was integrated using a Monkhorst-Pack grid of k-points, finer than 2π × 0.05 Å -1 spacing. A Gaussian smearing scheme with a smearing width of 0.20 eV was used during the electronic minimisation process. Vanderbilt ultrasoft pseudopotentials were used for computational efficiency (Tab. S3). The basis set included planewaves up to an associated kinetic energy of 1100 eV. Geometry optimisations converged until resultant forces were less than 0.05 eV/Å. The OptaDOS post-processing code was used to integrate individual Kohn-Sham eigenvalues into an electronic density of states, and the Matador high-throughput environment was used to obtain electronic band structure and density of states plots.