Closed-shell ring coupled cluster doubles theory with range separation applied on weak intermolecular interactions.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Accurate calculation of correlation energy is crucial for understanding molecular interactions.
• Coupled cluster theory provides accurate but computationally expensive methods.
• Random Phase Approximation (RPA) offers a more scalable alternative for correlation energy calculations.

Purpose of the Study:

• To explore and implement variants of the random phase approximation (RPA) for correlation energy.
• To combine long-range RPA with short-range density-functional approximations (DFAs) in a range-separated approach.
• To evaluate the performance of these methods for weakly interacting systems.

Main Methods:

• Implementation of different RPA variants derived from coupled cluster doubles theory.
• Application of range-separated density-functional theory (DFT) by combining long-range RPA with short-range DFAs.
• Testing on rare-gas dimers (He2, Ne2, Ar2) and the S22 molecular complex set.

Main Results:

• The two best-performing RPA variants were those originally proposed by Szabo and Ostlund.
• Range-separated RPA achieved mean absolute errors of approximately 0.4 kcal/mol on S22 equilibrium interaction energies.
• This corresponds to a mean absolute percentage error of about 4% using the aug-cc-pVDZ basis set.

Conclusions:

• Range-separated density-functional theory, combining long-range RPA with short-range DFAs, accurately predicts interaction energies for weakly interacting systems.
• The Szabo and Ostlund RPA variants show excellent performance in this context.
• This approach offers a promising balance between accuracy and computational cost for studying molecular interactions.