Advancing Non-Atom-Centered Basis Methods for More Accurate Interaction Energies: Benchmarks and Large-Scale...

Area of Science:

• Computational chemistry
• Quantum chemistry
• Theoretical chemistry

Background:

• Coupled cluster (CC) with single, double, and perturbative triple excitations (CCSD(T)) computations are crucial for accurate molecular modeling.
• Achieving the complete basis set (CBS) limit for large molecules is challenging due to basis set superposition errors.
• Non-atom-centered or floating orbitals (FOs) offer a potential solution but have practical limitations.

Purpose of the Study:

• To investigate a novel floating orbital (FO) approach for enhancing the accuracy of large-scale coupled cluster (CC) computations.
• To overcome limitations of existing FO methods, particularly for complex molecular systems.
• To reduce basis set errors in high-level electronic structure calculations.

Main Methods:

• Implementation of a double layer of FO centers with 4-9 FOs per center between interacting subsystems.
• Extension of double-zeta atomic orbital (AO) basis sets with the proposed FO method.
• Efficient local natural orbital CCSD(T) (LNO-CCSD(T)) calculations on molecules up to 72 atoms.

Main Results:

• The FO method, combined with double-zeta AO bases, achieves or surpasses the accuracy of conventional augmented double-zeta or triple-zeta AO bases.
• Basis set errors are reduced to a few tenths of a kcal/mol for medium-sized dimers.
• LNO-CCSD(T) calculations using the FO approach closely match LNO-CCSD(T)/CBS reference values (within ca. 0.1 kcal/mol).

Conclusions:

• The developed FO method effectively reduces basis set errors in large molecular complex calculations.
• This approach enables accurate modeling of large systems without atom-type limitations.
• Floating orbitals accelerate efficient correlation calculations, making high-accuracy computational chemistry more accessible.