Total energy calculations are performed using density functional theory as implemented within the Vienna ab initio simulation package (VASP). We use the projector augmented wave method and the PBEsol exchange-correlation functional . A plane wave cutoff of 550 eV is used for all calculations, and forces are relaxed to 1.0 meV Å-1 . For the Na 1 -x K x Cl solid solution, Gaussian smearing with a width of 0.05 eV is used, and a 6×6×6 Γ-centered k-point grid is used for the base cell, and scaled accordingly for larger supercells. For the Ag 1 -x Pd x solid solution, Methfessel-Paxton smearing with a width of 0.1 eV is used for the relaxations, while the final total energy is calculated with the tetrahedron method with Blöchl corrections. A 17×17×17 Γcentered k-point grid is used for the base cell, and scaled accordingly for larger supercells. For Ag 1 -x Pd x , spinpolarised calculations are performed initialised in the ferromagnetic state.