  We demonstrate that the Configuration Interaction (CI) Approximation
recaptures essential features of the exact (Bethe Ansatz) solution to the 1D
Hubbard model. As such, it provides valuable route for describing effects which
go beyond mean-field theory for strongly correlated electron systems in higher
dimensions. The CI method systematically describes fluctuation and quantum
tunneling corrections to the Hartree-Fock Approximation (HFA). HFA predicts
that doping a half-filled Hubbard chain leads to the appearance of charged
spin-polarons or charged domain-wall solitons in the antiferromagnetic (AFM)
background. The CI method, on the other hand, describes the quantum dynamics of
these charged magnetic solitons and quantum tunneling effects between various
mean-field configurations. In this paper, we test the accuracy of the CI method
against the exact solution of the one-dimensional Hubbard model. We find
remarkable agreement between the energy of the mobile charged bosonic
domain-wall (as given by the CI method) and the exact energy of the doping hole
(as given by the Bethe Ansatz) for the entire $U/t$ range. The CI method also
leads to a clear demonstration of the spin-charge separation in 1D. Addition of
one doping hole to the half-filled antiferromagnetic chain results in the
appearance of two different carriers: a charged bosonic domain-wall (which
carries the charge but no spin) and a neutral spin-1/2 domain wall (which
carries the spin but no charge).
