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Momentum Dependent Local-Ansatz Approach to Correlated Electron Systems: Non Half-Filled Case

Momentum dependent local-ansatz wavefunction approach (MLA) to the correlated electron systems in solids has been further developed to solve best a self-consistent equation for variational parameters at non half-filling. With use of the improved variational scheme we performed the numerical calculations for the non-half-filled band Hubbard model on the hypercubic lattice in infinite dimensions. We verified that the self-consistent scheme significantly improves the correlation energy and the momentum distribution as compared with the original scheme in the MLA. We also demonstrate that the theory improves the standard variational methods such as the Local-Ansatz approach (LA) and the Gutzwiller wavefunction approach (GA); the ground-state energy in the MLA is lower than those of the LA and the GA in the weak and intermediate Coulomb interaction regimes. The double occupation number is shown to be suppressed as compared with the LA. Calculated momentum distribution functions show a distinct momentum dependence, which is qualitatively different from those of the LA and the GA.