Explicitly correlated ring-coupled-cluster-doubles theory.

Area of Science:

• Quantum Chemistry
• Computational Physics
• Electronic-Structure Theory

Background:

• The random-phase approximation (RPA) is crucial in electronic-structure theory, linking density-functional and wave-function methods.
• RPA's broad applicability is hindered by slow basis-set convergence.

Purpose of the Study:

• To develop an explicitly correlated approach to RPA that overcomes slow basis-set convergence.
• To enhance the accuracy and efficiency of electronic-structure calculations.

Main Methods:

• An explicitly correlated approach based on the direct ring-coupled-cluster-doubles (CCDs) ansatz.
• Application of benchmark tests on 106 molecules and 10 organic complexes from the S22 set.

Main Results:

• Triple-zeta basis sets achieve 99% convergence for atomization energies.
• Quadruple-zeta basis sets are needed for interaction energies.
• Explicitly correlated corrections significantly reduce basis-set incompleteness error.

Conclusions:

• The presented explicitly correlated RPA method offers improved basis-set convergence.
• A non-iterative first-order perturbation correction provides an optimal balance of accuracy and computational cost.
• This method advances the accuracy of electronic-structure calculations.