Correlation energy in the He atom by Fulde's local approach

In the framework of calculations of electronic correlation energies some considerations are made on Fulde's Linearized Local Approach with emphasis on the comparison with the usual C.I. techniques. The particular rules proposed by Fulde in terms of the second quantization formalism to eliminate single excitation effects are analyzed and the equivalent C.I. wavefuntion is derived. Subsequently one presents the results of some computations of the correlation energy in the ground state of the He atom within the Local Approach and with a S.T.O. basis and one compares these results to the corresponding calculations performed by Fulde with a G.T.O. basis. Our results are slightly better than Fulde's because we have tried to optimize the ''regions'' and we have also frequently considered density-density correlations between different regions. The effectiveness of the Local Approach is confirmed provided that an optimized, or at least reasonable, choice of the ''regions'' is performed