Single-particle orbital ($\varphi$)

A single-particle wavefunction used as a mode of a many-particle description. An orbital can include spatial and spin variables; a spatial orbital specifies the spatial part. Orthonormal orbitals define creation and annihilation operators. Occupation of one normalized orbital by every boson gives a Hartree product state, while antisymmetrized occupation by fermions gives a Slater determinant.