  The choice of molecular orbitals is decisive in configuration interaction
calculations. In this letter, a democratic description of the ground and
excited states follows an orthogonally constrained orbitals optimization to
produce state-specific orbitals. The approach faithfully recovers the
excitation energy of afour-electron Hubbard trimer, whereas state-average
calculations can miss the value by a factor 2.5. The method emphasises the need
for orbitals optimizationto reduce expansions and to reach spectroscopic
accuracy.
