Jan Šmydke | Searcharxiv

arXiv2026

Preparing Small Gaussian Basis for Highly Accurate Ab Initio Description of Lithium Rydberg States

A new small and highly accurate Gaussian basis set has been developed for the ab initio description of $^2$Li Rydberg excited states up to $n = 7$ and S, P, D, F, and G angular momentum symmetry, and the appropriate optimization protocol is presented. The obtained Rydberg excitation energies are compared with results from other highly accurate approaches. At the EOM-CCSD level of theory the new basis exhibits higher than $10^{-2}$ eV accuracy of the excitation energies and the ionization potential and provides superior results than an analogous universal Gaussian basis set, while utilizing even smaller number of basis functions. Plots of the 1-dimensional Rydberg-orbital cuts reveal a regular nodal structure along the logarithmic scale of the atomic radius reaching tens of angstrom far from the nucleus. The presented Rydberg basis set generation methodology is an important step towards routine ab initio Rydberg-state related investigations of more complex systems, such as large atoms and polyatomic molecules.

physics.chem-ph↗

arXiv2022

Using Koopmans' theorem for constructing basis sets: Approaching high Rydberg excited states of lithium with a compact Gaussian basis

For accurate ab initio description of Rydberg excited states the study suggests generating the appropriate diffuse basis functions by a cheap variational optimization of virtual orbitals of the corresponding ion core. By following this approach, dozens of converged correlated lithium Rydberg states, namely all the states up to 24S, 25P, 14D, 16F and 16G, not yet achieved by other ab initio approaches, could be obtained at the EOM-CCSD level of theory with compact and mostly state-selective contracted Gaussian basis sets. Despite its small size and Gaussian character, the optimized basis leads to highly accurate excitation energies that differ merely in the order of meV from the reference state-of-the-art explicitly correlated Gaussian method and even surpass Full-CI results on Slater basis by an order of magnitude.

physics.chem-ph↗