Studies in multiconfiguration Dirac–Fock theory. Part 3.—Interpretation of the electronic structure of neutral and ionized states of uranium
Single manifold multiconfiguration Dirac–Fock calculations (average level) have been performed on the lowest manifolds, 5ƒ3 6d 7s2, 5ƒ3 6d2 7s(J= 6), in neutral atomic uranium and in the lowest manifolds of its ions up to U6+. Wave functions with not more than 30 configuration state functions were used. Studies of the energy distribution between effective one-electron energies, electron pair repulsions, and the like, illuminate the electronic structure of the ions, and explain, in particular, the reason why their ground states never contain more than three or four 5ƒ electrons. This is connected with their high angular momentum. As shown in previous studies of successive ionization, orbital relaxation plays only a minor role; there is no evidence of “charge sensitivity” of 5ƒ electrons in this context. Double manifold calculations (ƒ3ds2+ƒ3d2s in U, ƒ3s2+ƒ3ds in U+) show that the lowest levels of both systems are well mixed. Equivalent nonrelativistic calculations give a poor description of the ionization process.