A central theme in our analysis of the work presented in the A-lab paper, which we believe pertains more widely to the field of high-throughput computational material prediction, is the concept of order and disorder within a crystal lattice. The defining characteristic of a crystal lattice is order, but compositional disorder of atoms within a lattice is a widespread phenomenon. In fact, disorder in a crystal lattice is often used to tune the properties of a material, an example of which was recently demonstrated in Li 1.2 Cr 0.4 Mn 0.4 O 2 . Another example is the aforementioned Na 1-x K x Cl solid solution, which adopts the rock salt structure, with the Na and K atoms disordered over the cation sites. Physically, there is a statistical distribution of Na and K in the crystal -the probability of finding one particular cation in one particular location is based on the value of x in Na 1-x K x Cl. Such a system can be thought of as structurally ordered but compositionally disordered. Experimental crystallographers can accommodate compositional disorder within the framework of the unit cell description of the crystal, by simply stating that a single crystallographic site may be occupied by a mixture of multiple atom types with fractional occupancy. Thus, in crystallography, such a disordered system is represented with the same unit cell symmetry that would apply if there were only one atom type on the mixed site (i.e. the symmetry of the aristotype), but then specifying a fractional occupancy for some of the atoms. This description of compositionally disordered materials using partial occupancies has several advantages. Firstly, it is commensurate with the experimental diffraction patterns -the PXRD of Na 1-x K x Cl solid solutions resemble closely those of NaCl and KCl, but with only small shifts in peak positions and intensities, so it would make sense that the unit cell is very similar too. Secondly, fractional occupancies can be used in the structure factor equation to calculate diffraction intensities, this allows quantitative use of a unit cell with fractional occupancies for example in Rietveld refinement, while simple heuristics like Vegard's law relate the composition of a solid solution to the lattice parameter, usually with good accuracy. The usefulness of the idea of fractional occupancy, and its compatibility with many experimental crystallographic methods, is such that it is easy to overlook that in fact it breaks the foundational assumption of crystallography, that of transitional symmetry. As we will discuss below, this fact becomes much more significant when computational chemistry calculations are undertaken.