Theoretical Approaches to Direct Exchange Couplings between Divalent Chromium Ions in Naked Dimers, Tetramers, and Clusters
Theoretical Approaches to Direct Exchange Couplings between Divalent Chromium Ions in Naked Dimers, Tetramers, and Clusters
复制标题
裸二聚体、四聚体和簇中二价铬离子之间直接交换偶联的理论方法
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
K. Yamaguchi
中科院分区：
文献类型：
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作者：
M. Nishino;S. Yamanaka;Y. Yoshioka;K. Yamaguchi
从理论上研究了二价铬离子在裸二聚体、四聚体和团簇中的直接交换作用。用从头算UHF分子轨道方法和密度泛函方法计算了裸Cr(II)-−-Cr(II)二聚体(1)的轨道能隙、占位数和键级。所有这些计算表明，1的轨道能隙很小，因此由于强的电子关联效应，成键的σ，π和δ分子轨道和形式四键的占位数大大减少。对线性裸铬(II)四聚体进行了超高频和密度泛函分子轨道计算，阐明了d-−-d共轭体系可能的电子结构。根据基于UHF和DFT自然轨道(UNO)的CASCI和CASSCF方法得到的总能量计算了1的单重态、三重态和五重态之间的能量差。从理论上分析了海森堡模型哈密顿量的可靠性。
Direct exchange interactions between divalent chromium ions in naked dimers, tetramers, and clusters were investigated theoretically. The orbital energy gaps, occupation numbers, and bond orders for the naked Cr(II)−Cr(II) dimer (1) were calculated by ab initio UHF MO and density functional (DFT) methods. All these calculations indicated that the orbital energy gaps are very small for 1, and therefore the occupation numbers of the bonding σ, π, and δ molecular orbitals and formal quadruple bond orders were largely reduced because of strong electron correlation effects. The UHF and DFT MO calculations were also performed for the linear naked Cr(II) tetramer to elucidate possible electronic structures of the d−d conjugated systems. The energy differences among singlet, triplet, and quintet states for 1 were calculated from the total energies obtained by the CASCI and CASSCF methods based on the UHF and DFT natural orbitals (UNO). The reliability of the Heisenberg model Hamiltonian was elucidated from variat...