1. D. R. Hartree, “The Calculation of Atomic Structures”, (Wiley, New York, 1957).
2. E. U. Condon, and G. H. Shortley, “Theory of Atomic Spectra”, (Cambridge Univ. Press, 1935).
3. J. C. Slater, “Quantum Theory of Matter”, (McGraw Hill, New York, 1951).
4. P, A. M. Dirac, “The Principles of Quantum Mechanics”, (4th. ed., Oxford Univ. Press, 1958).
5. C. A. Coulson, “Valence”, (Oxford Univ. Press, 1961).