drawback, the unrestricted Hartree–Fock method is used frequently, and in preference to the restricted open-shell Hartree–Fock (ROHF) method, because UHF is simpler to code, easier to develop post-Hartree–Fock methods with, and returns unique functions unlike ROHF where different Fock operators can give the same final wave function. Unrestricted Hartree–Fock theory was discovered by Gaston Berthier and subsequently developed by John Pople; it is found in almost all ab initio programs. References Electronic structure methods