Parallel Calculation of Coupled Cluster Singles and Doubles Wave Functions Using Array Files.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Coupled Cluster Singles and Doubles (CCSD) is a high-level quantum chemistry method.
• Efficient parallel implementations are crucial for handling large molecular systems and basis sets.
• Existing methods may face limitations in scalability and computational cost.

Purpose of the Study:

• To introduce a novel parallel implementation of CCSD and related wave functions (QCI, CEPA).
• To demonstrate the program's capability to handle large basis sets on distributed memory clusters.
• To assess the computational efficiency and performance for large-scale electronic structure calculations.

Main Methods:

• Development of a parallel algorithm for CCSD and related methods using Array Files middleware.
• Formulation of major computational operations in terms of matrix multiplications for efficiency.
• Execution of calculations on distributed memory workstation clusters without extensive use of symmetry.

Main Results:

• The parallel implementation successfully handles large basis sets (up to 1512 basis functions) and numerous valence electrons (up to 228).
• High computational efficiency is achieved through matrix multiplication-based operations.
• Analysis of benzene dimer calculations indicates that MP2-based estimations for basis set enlargement effects in CCSD/QCISD are less reliable than assumed.

Conclusions:

• The new parallel implementation provides an efficient and scalable approach for advanced quantum chemical calculations.
• The findings challenge conventional methods for estimating basis set effects, suggesting a need for more accurate approaches.
• Replacing weak pair amplitudes with MP2 amplitudes in CCSD/QCISD calculations has a minimal impact on the calculated energy.