A judicious analysis of previously published experimental data leads one to conclude that the ground state of iron(II) phthalocyanine is an orbitally degenerate spin triplet $a_{ 1g}^2 e_g^{ \uparrow\downarrow\uparrow} b_{ 2g}^{ \uparrow}$ ($^3E_g$). The ligand field parameters, in relation to Racah's $C$, are approximately as follows: $B_{ 20}/C=0.84$, $B_{ 40}/C=0.0074$. The uniqueness of this result is demonstrated by means of a special diagram in the $B_{ 20}/C-B_{ 40}/C$ plane (under additional conditions that $B_{ 44}/B_{ 40}=35/3$ and $B/C=0.227$). The system is in a strong-ligand-field regime, which enables the use of single-determinant techniques corrected for correlations within the 3d shell of Fe.
Categories: cond-mat.mtrl-sci