Wavefunction-like Correlation Model for Use in Hybrid Density Functionals.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of molecular correlation energy is crucial for predicting chemical properties.
• Existing methods like Møller-Plesset perturbation theory (MP2) can be computationally expensive.
• Double-hybrid functionals offer improved accuracy but face challenges with basis-set convergence.

Purpose of the Study:

• To present Unsöld-W12 (UW12), a new approximation for the correlation energy of molecules.
• To introduce XCH-BLYP-UW12, a hybrid exchange-correlation functional incorporating UW12 correlation.
• To evaluate the performance of UW12 and XCH-BLYP-UW12 against established methods.

Main Methods:

• Developed UW12 as an explicit functional of the single-particle reduced-density matrix.
• Designed UW12 to resemble components of explicitly correlated second-order Møller-Plesset (MP2) theory.
• Formulated the XCH-BLYP-UW12 functional using UW12 correlation instead of MP2 correlation.

Main Results:

• UW12 exhibits straightforward orbital optimization and faster basis-set convergence compared to traditional double-hybrid functionals.
• XCH-BLYP-UW12 demonstrates higher accuracy than B2-PLYP for small-molecule main-group reaction barrier heights.
• XCH-BLYP-UW12 achieves accuracy comparable to B3LYP for atomization energies.

Conclusions:

• UW12 provides a computationally efficient alternative to MP2 correlation in double-hybrid functionals.
• The XCH-BLYP-UW12 functional presents a promising balance of accuracy and efficiency for quantum chemical calculations.
• This work advances the development of accurate and scalable methods for electronic structure calculations.