Method for determination of the fourth-rank zero field splitting parameters from the zero field energy levels for spin S̃ = 2 systems – Case studies: Fe2+ ions in [Fe(H2O)6](NH4)2(SO4)2 and forsterite (Fe2+:Mg2SiO4), and Cr2+ ions in (ND4)2Cr(D2O)6(SO4)2 and Rb2Cr(D2O)6(SO4)2