Small-Occupation Density Functional Correlation Energy Correction to Wave Function Approximations.

Area of Science:

• Quantum Chemistry
• Computational Chemistry

Background:

• Wave function theory (WFT) methods offer high accuracy but are computationally expensive.
• Density functional theory (DFT) provides a computationally cheaper alternative for correlation energy, but can lack accuracy.
• Bridging the gap between WFT and DFT is crucial for efficient and accurate electronic structure calculations.

Purpose of the Study:

• To introduce a novel hybrid method, WFT-soDFT, that integrates DFT correlation into WFT calculations.
• To improve the accuracy of electronic structure calculations in a computationally affordable manner.
• To explore the performance of WFT-soDFT for challenging chemical systems.

Main Methods:

• Developed WFT-soDFT by partitioning orbital space based on natural occupation numbers.
• Utilized a novel criterion to map electron density to correlation energy using a homogeneous electron gas model.
• Combined Restricted Active Space Configuration Interaction (RASCI) wave functions with hole and particle truncation.
• Employed a local density correlation functional to capture small-occupation correlation energy.

Main Results:

• WFT-soDFT demonstrated significant improvements over standard WFT calculations for small chemical systems.
• The method effectively incorporates DFT correlation energy into WFT ansatzes.
• The partitioning scheme and correlation functional choice were key to the method's success.

Conclusions:

• WFT-soDFT presents a computationally efficient strategy for enhancing WFT accuracy.
• The hybrid approach offers a promising avenue for more accurate electronic structure predictions.
• This method has the potential to advance computational chemistry for complex systems.