NEXAFS simulations with the CIS method can be significantly improved by using optimized core hole references. One aspect of these improvements is a different arrangement of the charge distribution after the core electron excitation. On page 116 (DOI: 10.1002/jcc.24531), Christopher Ehlert and Tillmann Klamroth explain that by using core hole optimized references (CHR), the resulting local positive charge can be efficiently shielded, which is energetically much more favorable. The image shows electron density differences for the excitation to the lowest core excited singlet states, negative iso-surfaces are colored red, positive ones blue.