Localized Molecular Orbitals for Single Excitation Theories

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Excited states in linked or stacked molecules are crucial for optoelectronic properties.
• These states manifest as local excitons (LEs) or charge transfer excitons (CTEs).
• Canonical molecular orbitals (CMOs) delocalize, complicating excited state analysis.

Purpose of the Study:

• To develop a straightforward method for analyzing excited states using localized molecular orbitals (LMOs).
• To ensure mathematical equivalence between calculations using LMOs and CMOs.
• To enhance the accessibility of qualitative and quantitative excited state analysis.

Main Methods:

• Employing LMOs derived from CMOs after self-consistent field calculations.
• Utilizing LMOs in configuration interaction singles (CIS), random phase approximation (RPA), and time-dependent density functional theory (TDDFT) calculations.
• Testing the approach on symmetric and asymmetric dimer systems.

Main Results:

• Excited state energies and transition moments are numerically identical between LMO and CMO calculations.
• LMOs provide a more accessible basis for analyzing LE and CTE contributions.
• The LMO approach is robust and numerically equivalent to CMOs for tested systems.

Conclusions:

• The LMO approach simplifies the analysis of excited states in molecular systems.
• This method facilitates the characterization of excitons in complex systems like multichromophores.
• The approach is valuable for studying electron and excitation energy transfer processes.