The Kohn–Sham equation is defined by a local effective (fictitious) external potential in which the non-interacting particles move, typically denoted as v s (r) or v eff (r), called the Kohn–Sham potential. If the particles in the Kohn–Sham system are non-interacting fermions (non-fermion Density Functional Theory has been researched), the Kohn–Sham wavefunction is a single Slater determinant constructed from a set of orbitals that are the lowest-energy solutions to ( − − ℏ ℏ 2 2 m ∇ ∇ 2 + v eff ( r ) ) φ φ i ( r ) = ε ε i φ φ i ( r ) .