Basis Set Limit of CCSD(T) Energies: Explicit Correlation Versus Density-Based Basis-Set Correction

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Basis-set incompleteness error is a significant challenge in wave function methods.
• Explicitly correlated and density-based correction approaches aim to mitigate this error.
• Previous methods often involve high computational costs.

Purpose of the Study:

• To compare explicitly correlated and density-based basis-set correction approaches.
• To present an efficient implementation of the density-based scheme using density-fitting.
• To evaluate the performance of these methods for MP2, CCSD, and CCSD(T) calculations.

Main Methods:

• Thorough comparison of explicitly correlated and density-based basis-set correction methods.
• Efficient implementation of density-based scheme with density-fitting approximation.
• Testing against complete basis set references for MP2, CCSD, and CCSD(T).

Main Results:

• Density-based correction with CABS-corrected Hartree-Fock energies is robust but does not outperform explicitly correlated methods.
• Density-corrected CCSD and CCSD(T) methods are computationally cheaper (roughly half the cost) than explicitly correlated variants.
• An incremental approach for CCSD and CCSD(T) using CABS correction and explicitly correlated MP2 contributions yields excellent results (<1 kcal/mol) with low computational expense.

Conclusions:

• Density-based corrections offer a computationally efficient way to reduce basis-set incompleteness error.
• Density-corrected coupled-cluster methods provide a competitive alternative to explicitly correlated methods due to reduced computational cost.
• The proposed incremental approach achieves high accuracy for thermochemical properties with minimal computational overhead.