A cumulant functional for static and dynamic correlation.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate modeling of electron correlation is crucial for predicting molecular properties.
• Existing density functionals face challenges in describing bond dissociation accurately.
• Cumulant functionals offer a potential pathway to improve correlation energy calculations.

Purpose of the Study:

• Introduce a novel functional for the cumulant energy.
• Develop a functional incorporating pair-correction, static, and dynamic correlation.
• Evaluate the functional's performance in modeling bond dissociation.

Main Methods:

• The functional utilizes natural orbitals and transferred occupancies for pair and static correlation.
• Dynamic correlation is based on the statically correlated on-top two-electron density.
• The Colle-Salvetti functional is employed for the on-top density functional.
• Calculations were performed using the cc-pVTZ basis set.

Main Results:

• The functional accurately models bond dissociation for H2, LiH, and N2.
• Obtained equilibrium bond lengths and dissociation energies are comparable to multireference perturbation theory.
• Performance is less accurate for HF and F2 due to underestimation of dynamic correlation.

Conclusions:

• The introduced cumulant functional shows significant potential for describing bond dissociation.
• Improvements in modeling dynamic correlation are needed for broader applicability.
• This work provides a foundation for developing more robust correlation functionals.