Cluster expansion of the wavefunction. Pseudohyphen;orbital theory based on the SAC expansion and its application to the spin density of openhyphen;shell systems

摘要

We have studied the pseudohyphen;orbital theory, which is based on the symmetryhyphen;adaptedhyphen;cluster (SAC) expansion of an exact wavefunction proposed previously, in comparison with the conventional openhyphen;shell orbital theories, and applied it to the calculations of the spin densities of the firsthyphen;row atoms, Li(2S), Li(2P), Be+(2S), B2+(2S), B(2P), C(3P), N(4S), O(3P), and F(2P). We have started from the RHF reference wavefunction and considered mainly the spinhyphen;polarization excitation operator and its selfhyphen;consistency effect. This pseudohyphen;orbital theory corresponds to an extension of the UHF and spinhyphen;extended HF (SEHF) theories, and yet it is free from the theoretical defects found previously for these theories. The relative magnitudes of the calculated spin densities are predicted to be in the order of the UHF or SEHF, present, and firsthyphen;order (FO) CI in the decreasing order. This sequence has been confirmed in the calculated spin densities for the firsthyphen;row atoms. For the threehyphen;electron atoms the present theory gives an excellent agreement with experiment, and for boron through fluorine the present results are fairly better than those of the UHF and SEHF theories and reasonable within the orbital theoretic approach. The calculated energies are also satisfactory when the angular correlation is included within the pseudohyphen;orbital theory.