Local explicitly correlated coupled-cluster methods: efficient removal of the basis set incompleteness and domain...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Basis set incompleteness and virtual orbital truncation introduce errors in quantum chemical calculations.
• Local approximations are essential for reducing computational cost in large molecular systems.
• Explicit correlation methods improve accuracy by including terms that depend explicitly on inter-electron distances.

Purpose of the Study:

• To develop a novel explicitly correlated local coupled cluster method (LCCSD-F12) that minimizes basis set incompleteness and local truncation errors.
• To enable accurate and computationally efficient calculations for large molecular systems.

Main Methods:

• Development of an explicitly correlated local LCCSD-F12 method incorporating explicitly correlated terms orthogonalized to pair-specific configuration spaces.
• Implicit inclusion of excitations outside local domains via explicitly correlated terms.
• Validation against a dataset of 54 reactions using triple-zeta basis sets.

Main Results:

• Reaction energies computed with the new LCCSD-F12 method show excellent agreement with conventional coupled cluster singles and doubles (CCSD) complete basis set results, with a maximum deviation of 2.5 kJ/mol (RMS: 0.6 kJ/mol).
• The method effectively reduces errors associated with basis set incompleteness and local approximations.
• The local approximations implemented are expected to yield linear scaling of computational cost with molecular size.

Conclusions:

• The proposed explicitly correlated local LCCSD-F12 method offers a significant advancement in computational quantum chemistry.
• This method provides highly accurate reaction energies while maintaining computational efficiency.
• The approach paves the way for accurate and scalable electronic structure calculations of large chemical systems.