Efficient implementation of molecular CCSD gradients with Cholesky-decomposed electron repulsion integrals

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Coupled cluster singles and doubles (CCSD) is a high-level quantum chemistry method for accurate molecular electronic structure calculations.
• Calculating gradients for CCSD is computationally intensive, posing a bottleneck for molecular geometry optimizations.

Purpose of the Study:

• To develop and implement an efficient computational scheme for ground and excited state CCSD gradients.
• To leverage Cholesky decomposition of electron repulsion integrals for improved computational performance.

Main Methods:

• Implementation of CCSD gradients utilizing Cholesky-decomposed electron repulsion integrals.
• Application of inner projection techniques to avoid large intermediate storage (e.g., V3O, V4 arrays).
• Avoidance of storing Cholesky vector derivatives.

Main Results:

• The new implementation achieves efficient calculation of CCSD gradients, with gradient computation taking less than 10% of total optimization time.
• Significant reduction in computational time per optimization cycle compared to previous inner projection methods.
• Successful geometry optimization of the retinal molecule (C20H28O) at the CCSD/aug-cc-pVDZ level.

Conclusions:

• The developed method offers a computationally efficient approach for CCSD gradient calculations.
• This advancement facilitates more feasible geometry optimizations for complex molecular systems.
• The implementation demonstrates practical utility in theoretical chemistry research.