S-wave resonances of positronic helium: all-electron study with the stabilization method

The positions and widths of six resonances in the positron−helium system, for the electronic spin singlet state, have been computed using the stabilization method. The penetrable, parameter-dependent confining potential has been included in the Hamiltonian, and the energy eigenvalues have been obtained in the optimized, fixed basis of explicitly correlated Gaussian functions. Apart from four already known resonances below the threshold for the formation of positronium in its first excited state, a new one has been revealed below the energy of the $4^{1}S$ state of the helium atom. The existence of the resonance formed by positron attachment to a doubly excited helium atom in the $2s^2$ electron configuration has also been confirmed. (paper)