State-interaction pair-density functional theory.

Area of Science:

• Computational chemistry
• Theoretical chemistry
• Quantum chemistry

Background:

• Accurately describing potential energy surfaces, especially with strong electronic state interactions, is a significant challenge for existing electronic structure methods.
• Understanding these interactions is vital for studying molecular processes like photochemistry and nonadiabatic dynamics.

Purpose of the Study:

• To develop a novel computational methodology capable of accurately describing ground- and excited-state potential energy surfaces in systems with strong electronic state interactions.
• To provide a robust tool for investigating complex molecular phenomena.

Main Methods:

• Introduction of state-interaction pair-density functional theory (SI-PDFT), an extension of multiconfiguration pair-density functional theory.
• Generation of N electronic states via diagonalization of an N x N effective Hamiltonian.
• Application of SI-PDFT to model systems: ionic-neutral avoided crossing in LiF and 1ππ-1πσ* avoided crossing in phenol photodissociation.

Main Results:

• SI-PDFT accurately describes regions with strong electronic state interactions.
• Calculations on LiF and phenol demonstrate the method's capability in handling avoided crossings.
• The study validates SI-PDFT as a reliable approach for complex molecular systems.

Conclusions:

• SI-PDFT offers a significant advancement in computational chemistry for studying systems with interacting electronic states.
• The method is a valuable tool for research in photochemistry and nonadiabatic dynamics.
• This work paves the way for more accurate simulations of excited-state processes.