The ANO-R Basis Set.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate quantum chemical calculations require efficient and reliable basis sets.
• Existing basis sets may lack compactness or universal applicability for both light and heavy elements.

Purpose of the Study:

• Introduce the novel ANO-R basis set for comprehensive elemental coverage.
• Develop a compact and accurate basis set suitable for scalar-relativistic effects and Gaussian nucleus modeling.

Main Methods:

• Developed an all-electron basis set incorporating exact-two component (X2C) Hamiltonian scalar-relativistic effects.
• Modeled atomic nuclei using a Gaussian charge distribution for broad elemental applicability.
• Utilized the general contraction scheme and CASSCF/CASPT2 level of theory for high accuracy.
• Optimized primitive basis functions based on convergence to the complete basis set limit.
• Employed the density-averaged atomic-natural-orbital (ANO) scheme for contraction, guided by natural orbital occupation numbers.

Main Results:

• The ANO-R basis set offers a unique, element-specific composition (ANO-R0 to ANO-R3) balancing compactness and quality.
• It avoids superfluous functions, ensuring efficiency without compromising accuracy.
• The basis set is balanced across the first six periods (H-Rn).

Conclusions:

• The ANO-R basis set provides a computationally efficient and accurate tool for electronic structure calculations.
• Its design makes it suitable for a wide range of elements, including heavy ones.
• This basis set advances the capability for high-accuracy quantum chemical modeling.