Considerations of natural orbital decompositions of H₂for double photoionization investigations

Recently, we have investigated the role of electron correlation in double photoionization studies using a natural orbital decomposition of fundamental two-electron systems: atomic helium and molecular H₂ [1]. The latter molecular target reveals much more sensitivity to the natural orbitals accounted for in the description of the intitial state, requiring substantially more correlating configurations be included compared to helium.  Here we will further explore the consequences of basis set accuracy and completeness in representing the H₂ bound state, paying particular attention to the gauge dependence of the double photoionization cross sections and the resulting angular distributions.

[1] Phys. Rev. A 99, 013403 (2019).