Table shows atomic SOCCs. For atoms Eq. ( ) no longer gives a rotationally invariant constant. Therefore, here we summed the matrix elements not only by spin projections, but also by the projections of orbital angular momentum. This also leads to large atomic SOCCs. These values can be compared with experimental data within Landé interval rule , as explained below. To compare these values with experiment, one should divide the SOCC by L(L + 1) S(S + 1). The resulting quantity can be compared with Russell-Sauders LS coupling constant (ζ) extracted from splittings through Landé interval rule . For example, SOMF gives an estimate for 5 D g levels of Mn + of ζ = 68.29 cm -1 , while the values extracted from experiment are within 58.66-66.99 cm -1 interval . The averaged experimental value of ζ for Fe 2+ is 100 cm -1 , while the SOMF estimate from Table The SMM studied in Ref. has d 6 electronic configuration, corresponding the overall negative charge. As explained below, this electronic configuration gives to electronic degeneracy and Jahn-Teller distortions. EOM-CC methods are capable of tackling Jahn-Teller and pseudo-Jahn-Teller effects very well , however, this particular system is different and its description is affected by the non-Hermitian nature of EOM-CC theory .