Valence ππ* Excitations in Benzene Studied by Multiconfiguration Pair-Density Functional Theory

Area of Science:

• Quantum chemistry
• Computational chemistry
• Theoretical chemistry

Background:

• Accurate calculation of electronic excitations is crucial in chemistry.
• Benzene's ππ* excitations are fundamental for understanding its electronic structure.
• Existing methods may require refinement for complex electronic states.

Purpose of the Study:

• To investigate benzene's singlet and triplet ππ* excitations.
• To develop a novel method for quantifying electronic state character.
• To assess the impact of density functional components on excitation energy calculations.

Main Methods:

• Complete Active Space Self-Consistent Field (CASSCF) theory.
• Complete Active Space Perturbation Theory (CASPT2).
• Multiconfiguration Pair-Density Functional Theory (MC-PDFT) with varied active spaces and density functional components.

Main Results:

• Quantification of covalent and ionic character in electronic states.
• Improved accuracy of MC-PDFT excitation energies for benzene with increased exchange contribution.
• Systematic exploration of excitation energies across different theoretical methods and active spaces.

Conclusions:

• The proposed energy component analysis provides new insights into electronic state character.
• Tuning density functional exchange improves MC-PDFT performance for benzene excitations.
• CASSCF, CASPT2, and MC-PDFT offer complementary approaches for studying electronic excitations.