Orthogonally Constrained Orbital Optimization: assessing changes of optimal orbitals for orthogonal multi-reference states

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 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.

References in corpus (4)

• The density matrix renormalization group for ab initio quantum chemistry
• Delta Self-Consistent Field as a method to obtain potential energy surfaces of excited molecules on surfaces
• Orbital Optimization in Selected Configuration Interaction Methods
• Tailoring CIPSI expansions for QMC calculations of electronic excitations: the case study of thiophene

Cited by in corpus (1)

• Orthogonally Constrained CASSCF Framework: Newton-Raphson Orbital Optimization and Nuclear Gradients