  The wavefunction method provides us with a useful tool to describe electron
correlations in solids at the ground state. In this paper we review the recent
development of the momentum-dependent local ansatz wavefunction (MLA). It is
constructed by taking into account two-particle excited states projected onto
the local orbitals, and the momentum-dependent amplitudes of these states are
chosen as variational parameters. The MLA describes accurately correlated
electron states from the weak to the intermediate Coulomb interaction regime in
infinite dimensions, and works well even in the strongly correlated region by
introducing a new starting wavefunction called the hybrid (HB) wavefunction.
The MLA-HB is therefore shown to overcome the limitation of the original local
ansatz (LA) wavefunction as well as the Gutzwiller wavefunction. In particular,
the calculated quasiparticle weight vs Coulomb interaction curve is shown to be
close to that obtained by the numerical renormalization group approach. It is
also shown that the MLA is applicable to the first-principles Hamiltonian.
