Addressing the System-Size Dependence of the Local Approximation Error in Coupled-Cluster Calculations

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Method Development

Background:

• Coupled-cluster singles and doubles with perturbative triples (CCSD(T)) is the gold standard for accurate electronic structure calculations.
• Local approximations have extended CCSD(T) to large systems but introduce errors that scale with system size.
• Pair Natural Orbitals (PNOs) are crucial for the efficiency of local coupled-cluster methods.

Purpose of the Study:

• To investigate a novel two-point extrapolation scheme for domain-based PNO-CCSD(T) calculations.
• To reduce the dependence of local approximation errors on system size.
• To enable benchmark-quality energy calculations for large molecular systems.

Main Methods:

• Implementation of a two-point extrapolation scheme within the domain-based PNO-CCSD(T) framework.
• Systematic study of the impact of the extrapolation scheme on the error behavior with increasing system size.
• Calculation of relative energies for model systems to assess accuracy.

Main Results:

• The two-point extrapolation scheme drastically reduces the error dependence on system size.
• Extrapolated results show significantly improved accuracy compared to non-extrapolated local approximations.
• The method allows for accurate calculations of relative energies in large systems.

Conclusions:

• The developed two-point extrapolation scheme effectively mitigates system-size-dependent errors in PNO-CCSD(T) calculations.
• This advancement opens new avenues for high-accuracy computational chemistry on large molecular systems.
• Benchmark quality relative energies can now be obtained for previously intractable system sizes.