Ab initio computations of zero-field splitting parameters and effective exchange integrals for single-molecule magnets (Mn-12- and Mn11Cr-acetate clusters)

作者：Sano Shinsuke; Kawakami Takashi^*; Yoshimura Shohei; Shoji Mitsuo; Yamanaka Shusuke; Okumura Mitsutaka; Nakajima Takahito; Yamaguchi Kizashi

来源：Polyhedron, 2017, 136: 159-169.

DOI：10.1016/j.poly.2017.03.047

• Mn-12-acetate clusters
• Single-molecule magnets
• Zero-field splitting
• Effective exchange integral
• Ab initio MO method

In this study, the zero-field splitting parameters (D, E) and effective exchange integrals (J) for a Mn-12/Mn11Cr mixed crystal were evaluated using ab initio molecular orbital (MO) computations based on the hybrid density functional theory (DFT) methods for MniiCe-acetate cluster (Mn-12 and Mn11Cr mixing). In this study, Mn-12-acetate, Mn11Cr-acetate, and Mn12-nCrn-acetate clusters were focused on. The zero-field splitting (ZFS) parameters are obtained by UB3LYP methods, i.e. 0.339 cm(-1) (Mn-12-acetate) and 0.351 cm(-1) (Mn11Cr-acetate). The energy barriers were estimated to be 53.7 K and 50.4 K, which showed good agreement with previously reported experimental values of 68.8 K and 56.8 K, respectively. The origin of such anisotropy is assumed to be the eight Me ions with d(4)-electrons in their outer ring subunits, where elongated conformation along the axial direction becomes very important and leads to negative D values. The spin networks in these clusters were discussed by using the effective exchange integral sets. The Js value, as estimated by the UB3LYP method revealed that the J(2), J(3), and J(3) interactions played important roles in describing the parallel spin ordering in cubane and ring subunits as well as the antiferromagnetic coupling between two subunits. The other interactions, i.e. J(1), J(1)', J(4), and J(4) somewhat disturbed the spin ordering in the Mn-12-acetate cluster. The substitution of Mn-IV by Cr-III did not change the spin network. However, the total S value changed after the substitution.

• 出版日期2017-11-4
• 单位RIKEN