Generalized-active-space pair-density functional theory: an efficient method to study large, strongly correlated,...

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• Accurate prediction of ground- and excited-state properties for open-shell organic molecules is challenging due to complex electron correlation.
• Strongly correlated systems, exhibiting near-degeneracy effects, pose significant difficulties for standard electronic structure methods.
• Existing multiconfigurational wave function methods struggle with dynamic correlation in large active spaces.

Purpose of the Study:

• To introduce and validate multiconfiguration pair-density functional theory (MC-PDFT) for strongly correlated organic systems.
• To calculate singlet-triplet gaps in oligoacenes using MC-PDFT with large active spaces.
• To assess the performance of MC-PDFT against established, computationally intensive methods.

Main Methods:

• Development and application of multiconfiguration pair-density functional theory (MC-PDFT).
• Calculation of singlet-triplet gaps for oligoacenes from naphthalene to dodecacene.
• Utilized large, orbitally optimized active spaces (50 electrons in 50 orbitals) and tested various active space partitions.

Main Results:

• MC-PDFT successfully computed singlet-triplet splittings for oligoacenes.
• Results obtained were consistent with high-level, more computationally expensive methods.
• Demonstrated the capability of MC-PDFT to handle large active spaces with significant static and dynamic correlation.

Conclusions:

• MC-PDFT provides a practical and accurate approach for predicting properties of strongly correlated open-shell organic molecules.
• The method shows promise as a benchmark for evaluating other electronic structure models in the absence of experimental data.
• MC-PDFT effectively combines the strengths of wave function theory and density functional theory.