A Guided Self-Consistent-Field Method for Excited-State Wave Function Optimization: Applications to Ligand-Field...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Self-Consistent Field (SCF) methods are crucial for electronic structure calculations.
• Optimizing higher-energy solutions (excited states) to the Roothaan-Hall equation presents convergence challenges.
• Accurate calculation of excitation energies is vital for understanding chemical and physical properties.

Purpose of the Study:

• To present a novel guided self-consistent field (SCF) method for improved wave function optimization.
• To enhance the calculation of excited states, particularly those with the same spin symmetry as the ground state.
• To improve the stability and convergence of SCF calculations for complex systems.

Main Methods:

• The guided SCF method utilizes an eigenspace update-and-following strategy.
• Prediagonalization of the Fock/Kohn-Sham matrix using previous eigenvectors preserves orbital occupations.
• A preconditioning step involving SCF iteration on the beta spin manifold improves initial guesses for excited states.

Main Results:

• The guided SCF method demonstrates more stable convergence compared to standard SCF approaches.
• Application to tetrahedral transition-metal complexes accurately optimizes ligand-field excited states.
• Calculated ΔSCF excitation energies show significant improvement over orbital energy differences and linear response methods.

Conclusions:

• The guided SCF method offers a robust and accurate approach for electronic structure calculations of excited states.
• This method provides a valuable tool for computing excitation energies in transition-metal complexes.
• The findings suggest potential for broader applications in computational chemistry and materials science.