Ab initio molecular orbital studies of possibility the ferromagnetic ordering in the isoelectron-substituted ferrocarbon modifications

For investigation of possibility the ferromagnetic ordering in some isoelectron-substituted ferrocarbon modifications ab initio calculations of the vertical singlet-triplet (ST) splitting in C3H6, C2BH6-, C2NH6+, C2BeH62− were performed at MP4SDTQ/6-311G∗∗ level. The molecular geometry either corresponded to the UHF/6-31G∗ energy minimum of the triplet electron configuration, or extracted from the ferrocarbon crystal. For all considered structures it has been found, that fourth-order Moller-Plesset method requires the taking into account of triple excitations for obtaining more reliable ST splitting values. Obtained results prove the presence of the ferromagnetic ordering in the C3H6, C2BH6-, C2NH6+, while the lowest (S) and (T) states of C2BeH62− appear to be quasidegenerate.