Configuration-interaction method with Hylleraas-Gaussian-type basis functions in cylindrical coordinates: Helium atom in a strong magnetic field

Abstract

The energy levels involving the $^{1}0^{+}$, $^{1}(\ensuremath{-}1)^{+}$, and $^{1}(\ensuremath{-}2)^{+}$ states of the helium atom in strong magnetic fields up to $2.35\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ are investigated. Our computational approach is a configuration-interaction (CI) method based on a set of anisotropic Hylleraas-Gaussian orbitals nonlinearly optimized for different field strength. A detailed comparison between our method and the CI method with the Gaussian-type basis functions in cylindrical coordinates is made. The advantages of the Hylleraas-Gaussian basis over the Gaussian basis are discussed.