Efficient Implementation of Equation-of-Motion Coupled-Cluster Singles and Doubles Method with the Density-Fitting...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) is a powerful method for calculating excitation energies.
• The particle-particle ladder (PPL) term is computationally the most expensive part of EOM-CCSD calculations.
• Existing methods like resolution of the identity EOM-CCSD (RI-EOM-CCSD) face computational challenges for large systems.

Purpose of the Study:

• To develop and implement an efficient density-fitted EOM-CCSD (DF-EOM-CCSD) method.
• To enhance the evaluation of the computationally intensive PPL term.
• To introduce a hybrid density-fitting/Cholesky decomposition (DF/CD) algorithm for further optimization.

Main Methods:

• Implementation of an enhanced algorithm for the particle-particle ladder (PPL) term in DF-EOM-CCSD.
• Introduction of a hybrid density-fitting/Cholesky decomposition (DF/CD) approach for integral evaluation.
• Comparison of computational costs and efficiency against RI-EOM-CCSD for excitation energy calculations.

Main Results:

• DF-EOM-CCSD shows significant acceleration in excitation energy calculations compared to RI-EOM-CCSD.
• A 2-fold reduction in computational cost was observed for C8H18 using a restricted Hartree-Fock (RHF) reference.
• The hybrid DF/CD approach demonstrates improved performance, particularly for large molecular systems.

Conclusions:

• The developed DF-EOM-CCSD method with the hybrid DF/CD PPL algorithm offers substantial computational savings.
• This approach is highly efficient for calculating excitation energies, outperforming RI-EOM-CCSD.
• The new algorithm is a promising tool for tackling large-sized chemical systems in computational chemistry.