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 orbital optimization to… Click to show full abstract
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 orbital optimization to produce state-specific orbitals. The approach faithfully recovers the excitation energy of a four-electron Hubbard trimer, whereas state-average calculations can miss the value by a factor 2.5. The method emphasizes the need for orbital optimization to reduce configuration interaction expansions and to reach spectroscopic accuracy.
               
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