A cross-entropy corrected hybrid multiconfiguration pair-density functional theory for complex molecular systems.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Hybrid density functionals (e.g., B3LYP, PBE0) offer significant improvements over parent methods.
• Second-order Møller-Plesset perturbation theory (MP2) is computationally expensive.
• Existing hybrid multiconfiguration pair-density functional theory (HMC-PDFT) methods have limitations.

Purpose of the Study:

• To extend the linear scheme of HMC-PDFT by incorporating a cross-entropy ingredient.
• To develop a new functional, tB4LYP, that balances static and dynamic correlation.
• To improve the accuracy of exchange and correlation energies.

Main Methods:

• Extension of the linear scheme of HMC-PDFT.
• Incorporation of a cross-entropy ingredient.
• Development of the tB4LYP functional.

Main Results:

• tB4LYP consistently improves exchange and correlation energies.
• tB4LYP outperforms parent methods (CASSCF) and original MC-PDFT functionals (tBLYP, tB3LYP).
• tB4LYP surpasses the accuracy of CASPT2 for challenging chemical systems like Cr2 dissociation and torsional rotations, at a lower computational cost.

Conclusions:

• The developed tB4LYP functional offers superior accuracy for challenging cases.
• tB4LYP provides a more balanced description of static and dynamic correlation.
• This method presents a computationally efficient alternative to CASPT2 for complex chemical problems.