Pierloot Kristine, Vancoillie Steven
Department of Chemistry, University of Leuven, Celestijnenlaan 200F, B-3001 Heverlee-Leuven, Belgium.
J Chem Phys. 2006 Sep 28;125(12):124303. doi: 10.1063/1.2353829.
High-level ab initio calculations using the CASPT2 method and extensive basis sets were performed on the energy differences of the high-[(5)T(2g):t(2g) (4)e(g) (2)] and low-[(1)A(1g):t(2g) (6)] spin states of the pseudo-octahedral Fe(II) complexes Fe(H(2)O)(6), Fe(NH(3))(6), and Fe(bpy)(3). The results are compared to the results obtained from density functional theory calculations with the generalized gradient approximation functional BP86 and two hybrid functionals B3LYP and PBE0, and serve as a calibration for the latter methods. We find that large basis set CASPT2 calculations may provide results for the high-spin/low-spin splitting DeltaE(HL) that are accurate to within 1000 cm(-1), provided they are based on an adequately large CAS[10,12] reference wave function. The latter condition was found to be much more stringent for Fe(bpy)(3) than for the other two complexes. Our "best" results for DeltaE(HL) (including a zero-point energy correction) are -17 690 cm(-1) for Fe(H(2)O)(6), -8389 cm(-1) for Fe(NH(3))(6), and 3820 cm(-1) for Fe(bpy)(3).
使用CASPT2方法和广泛的基组对八面体伪铁（II）配合物[Fe(H₂O)₆]²⁺、[Fe(NH₃)₆]²⁺和[Fe(bpy)₃]²⁺的高自旋态[(⁵)T₂g:t₂g⁴e g²]和低自旋态[(¹)A₁g:t₂g⁶]之间的能量差进行了高水平的从头计算。将结果与使用广义梯度近似泛函BP86以及两种杂化泛函B3LYP和PBE0从密度泛函理论计算中获得的结果进行了比较，并为后一种方法提供了校准。我们发现，只要基于足够大的CAS[10,12]参考波函数，大基组CASPT2计算就可以提供高自旋/低自旋分裂ΔE(HL)的结果，其精度在1000 cm⁻¹以内。结果发现，对于[Fe(bpy)₃]²⁺，后一个条件比其他两种配合物更为严格。我们对于ΔE(HL)的“最佳”结果（包括零点能校正）是：对于[Fe(H₂O)₆]²⁺为-17690 cm⁻¹，对于[Fe(NH₃)₆]²⁺为-8389 cm⁻¹，对于[Fe(bpy)₃]²⁺为3820 cm⁻¹。
