with the single-electron kinetic energy operator T ^ ^ s , the effective potential V eff ( r ) , Kohn-Sham states Ψ Ψ j k ( r ) , energy eigenvalues ϵ ϵ j k , and position and Bloch vectors r and k . While in abstract evaluations of Kohn-Sham DFT the model for the exchange-correlation contribution to the effective potential is the only fundamental approximation, in practice solving the Kohn-Sham equations is accompanied by the introduction of many additional approximations. These include the incompleteness of the basis set used to represent the Kohn-Sham orbitals, the choice of whether to use the pseudopotential approximation or to consider all electrons in the DFT scheme, the treatment of relativistic effects, and possible shape approximations to the potential. Beyond the partitioning of the unit cell, for the LAPW method the central design aspect is the use of the LAPW basis set { ϕ ϕ k , G ( r ) } to represent the valence electron orbitals as