Relativistic quintuple-zeta basis sets for the s block
Marten L. Reitsma, Eifion H. Prinsen, Johan D. Polet, Anastasia Borschevsky, Kenneth G. Dyall
TL;DR
This work addresses the need for high-accuracy relativistic basis sets for the s-block to enable precision calculations of heavy-element systems. It develops quintuple-zeta basis sets with SCF exponents for occupied spinors and the np shell, MR-SDCI-optimized valence/core correlating functions, diffuse functions for anions, and outer-core polarization functions, employing a novel even-tempered exponent strategy to stabilize 5z optimization and a cc1-like framework for correlating spaces. Benchmarking on IPs, EAs, bond lengths, and dissociation energies demonstrates smooth convergence to the complete basis set limit from 4z to 5z and good agreement with experimental data where available, illustrating the practical value of these bases when paired with state-of-the-art relativistic and correlation methods. The results indicate that these 5z sets can deliver higher accuracy and lower uncertainty for heavy-atom calculations, with broad applicability to fundamental-physics experiments and heavy-element chemistry; the basis sets are publicly available for community use and refinement. $E_N^{\mathrm{corr}} = E_{\mathrm{CBS}}^{\mathrm{corr}} + \frac{A}{N^3}$ is used for correlation-energy extrapolation, highlighting the quantitative path to CBS accuracy.$
Abstract
Relativistic basis sets of quintuple-zeta quality are presented for the s-block elements. The basis sets include SCF exponents for the occupied spinors and for the np shell (the latter is considered here a valence orbital). Valence and core correlating functions were optimized within multireference SDCI calculations for the ground valence configuration. Diffuse functions optimized for the corresponding anions or derived from neighboring elements are also provided. The new basis sets were applied to a range of basic atomic and molecular properties for benchmarking purposes. Smooth convergence to the basis set limit is observed with increased basis set quality from existing double-zeta, triple-zeta, and quadruple-zeta to the newly developed quintuple-zeta basis sets. Use of these basis sets in combination with state-of-the-art approaches for treatment of relativity and correlation will allow achieving higher accuracy and lower uncertainty than previously possible in calculations on heavy atoms and molecules. The basis sets are available at https://doi.org/10.5281/zenodo.17088050.