Effect of local structure on electron paramagnetic resonance spectra for trigonal [Cr(H2O)6]3+coordination complex in the sulfate alums series: a ligand field theory study

A simple theoretical method is introduced for studying the interrelation between electronic and molecular structures. By diagonalizing the $120\times 120$ complete energy matrices, the relationships between zero-field splitting (ZFS) parameter $D$ and local distortion parameter $\Delta \theta $ for Cr$^{3 + }$ ions doped, separately, in $\alpha$- and $\beta$- alums are investigated. Our results indicate that there exists an approximately linear relationship between $D$ and $\Delta \theta $ in a temperature range 4.2--297~K and the signs of $D$ and $\Delta \theta $ are opposite to each other. Moreover, in order to understand the contribution of spin--orbit coupling coefficient $\zeta $ to ZFS parameter $D$, the relation between $D$ and $\zeta $ is also discussed.