A straightforward generalization of the HF method is the Multicomponent Unrestricted Hartree-Fock (muHF or µHF or µSCF). In this method we consider two or more different kinds of Fermions, e.g. protons and electrons, in a single SCF procedure. This method was introduced as Nuclear Electron Orbital (NEO) method and extensively developed by the Hammes-Schiffer group starting with . Because this method makes no restriction to the kind of Fermion, e.g. nuclei xor positrons, I prefer the Multicomponent SCF name, e.g. µHF if correlation is entirely absent. One important consideration is the basis set. Electronic structure theory has developed many basis sets for electrons in a variety of conditions (many of these are stored on the Basis Set Exchange, see ). However, other Fermions have not gotten the same treatment. Naïvely, the exponential-value of the basis-set parameters controls the scale of the basis, changing these introduces a new length-scale. This length-scale is controlled by the mass of the Fermion. Thus, suppose ζ 0 is the exponential of Gaussian-fitted-Slater functions, then ζ = ζ0 M 2 is the exponential factor for a particle of mass M . However, unlike atomistic basis functions which expect a wavefunction solution for the inverse-distance potential of the nuclei e.g. V (r) = 1 4πε0ε 1 r , it is well-known that nuclei experience more of a harmonic-potential (parabolic), i.e. corresponding to vibrational frequencies. Because nuclei are well-separated in regular matter, they are always in singly occupied states. Therefore specialized basis functions should be used. In conjunction of introducing the method, Hammes-Schiffer's group introduced protonic basis-functions, see and density-functionals .