Accurate Reduced-Cost CCSD(T) Energies: Parallel Implementation, Benchmarks, and Large-Scale Applications.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Method Development

Background:

• Coupled-Cluster Singles, Doubles, and Perturbative Triples [CCSD(T)] is a high-accuracy quantum chemistry method.
• Computational cost limits the application of canonical CCSD(T) to small molecular systems.
• Frozen Natural Orbital (FNO) and Natural Auxiliary Function (NAF) approaches offer significant cost reductions.

Purpose of the Study:

• To implement and benchmark combined Frozen Natural Orbital (FNO) and Natural Auxiliary Function (NAF) approximations with Coupled-Cluster Singles, Doubles, and Perturbative Triples [CCSD(T)].
• To assess the accuracy and scalability of the developed FNO-CCSD(T) method for various chemical properties and system sizes.
• To extend the applicability of accurate electronic structure calculations to larger and more complex molecular systems.

Main Methods:

• Integration of FNO and NAF approximations into existing CCSD(T) codes.
• Implementation of OpenMP parallelism, integral-direct density-fitting, and checkpointing for efficiency.
• Benchmarking against canonical CCSD(T) for reaction, atomization, and ionization energies of closed- and open-shell species.

Main Results:

• FNO-CCSD(T) maintains chemical accuracy (within 1 kJ/mol) compared to canonical CCSD(T) for systems up to 43 atoms.
• Computational cost is reduced by up to an order of magnitude, enabling calculations for systems with 50-75 atoms.
• The method demonstrates excellent parallel performance and high peak performance utilization on hundreds of cores.

Conclusions:

• The developed FNO-CCSD(T) method provides a computationally feasible route to "gold standard" accuracy for significantly larger systems.
• This advancement expands the accessible chemical space for high-accuracy electronic structure calculations.
• Potential applications include benchmarking other computational methods and studying complex chemical reactions and interactions.