Electronic Excitation Energy Calculations with Configuration Interaction Based on Nonorthogonal Localized Molecular...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Conventional configuration interaction (CI) methods rely on canonical Hartree-Fock molecular orbitals.
• Configuration interaction with single excitation states (CIS) is a common method for excited-state calculations.
• Nonorthogonal localized molecular orbitals (NOLMOs) have been developed for efficient electronic structure calculations.

Purpose of the Study:

• To develop and explore a novel method combining CI with NOLMOs for electronic excited-state calculations.
• To investigate the performance of this new method, termed NOLMO-CIS, compared to existing approaches.
• To assess the potential of NOLMOs for correlated electronic structure calculations in large systems.

Main Methods:

• Developed a configuration interaction (CI) method based on nonorthogonal localized molecular orbitals (NOLMOs).
• Generated excited-state configurations by substituting occupied NOLMOs with virtual NOLMOs, determined via variational calculations.
• Employed a state-averaged approach to minimize ground and excited-state energies while maintaining wave function orthogonality.

Main Results:

• The number of excited determinants in NOLMO-CIS is equal to the number of electrons (N), independent of basis functions.
• NOLMO-CIS captures significant electron correlation for ground-state calculations but is not size consistent.
• NOLMO-CIS demonstrates superior performance over conventional CIS and time-dependent DFT for excited-state calculations in small molecules.

Conclusions:

• The combination of CI with NOLMOs (NOLMO-CIS) presents a promising advancement for electronic excited-state calculations.
• This method offers improved accuracy and efficiency compared to traditional methods like CIS and TD-DFT.
• NOLMO-based correlated electronic structure calculations represent a significant step towards efficient computational methods for large molecular systems.