Møller-Plesset and Density-Fixed Adiabatic Connections for a Model Diatomic System at Different Correlation Regimes

Area of Science:

• Quantum chemistry
• Computational physics
• Materials science

Background:

• Adiabatic connection (AC) methods within density functional theory (DFT) show promise for calculating interaction energies using Hartree-Fock (HF) ingredients.
• Previous studies explored the strong-interaction limit of Møller-Plesset (MP) AC to understand DFT's performance.

Purpose of the Study:

• To investigate the behavior of both MP and DFT AC integrands for the asymmetric Hubbard dimer.
• To systematically explore different correlation regimes by varying external potential (Δv) and interaction strength (U).
• To analyze the second-order expansion of correlation energy and the derivative of the λ-dependent density.

Main Methods:

• Calculation of MP and DFT AC integrands for the asymmetric Hubbard dimer.
• Systematic variation of external potential (Δv) and interaction strength (U).
• Analysis of the strong-interaction limit for both MP and DFT ACs.

Main Results:

• The DFT AC integrand exhibits convexity across the parameter space.
• The MP AC integrand can display up to two changes in curvature.
• The derivative of the λ-dependent density in MP AC at λ=0 is zero for the model.
• Asymptotic values of MP AC (W∞HF) are lower than or equal to DFT AC (W∞KS) at a given density, but not always at a given external potential.

Conclusions:

• The study provides insights into the differences between MP and DFT AC methods in various correlation regimes.
• Understanding these differences is crucial for accurate calculation of interaction energies.
• The findings contribute to the theoretical foundation of DFT and AC methods in electronic structure calculations.