Lawson Daku Latévi Max, Vargas Alfredo, Hauser Andreas, Fouqueau Antony, Casida Mark Earl
Département de Chimie physique, Université de Genève, 30 quai Ernest-Ansermet, 1211 Genève 4 Switzterland.
Chemphyschem. 2005 Jul 11;6(7):1393-410. doi: 10.1002/cphc.200400584.
In the iron(II) low-spin complex [Fe(bpy)3]2+, the zero-point energy difference between the 5T2g(t4(2g)e2g) high-spin and the 1A(1g)(t(6)2g) low-spin states, Delta(E)0HL, is estimated to lie in the range of 2500-5000 cm(-1). This estimate is based on the low-temperature dynamics of the high-spin-->low-spin relaxation following the light-induced population of the high-spin state and on the assumption that the bond-length difference between the two states Delta(r)HL is equal to the average value of approximately 0.2 A, as found experimentally for the spin-crossover system. Calculations based on density functional theory (DFT) validate the structural assumption insofar as the low-spin-state optimised geometries are found to be in very good agreement with the experimental X-ray structure of the complex and the predicted high-spin geometries are all very close to one another for a whole series of common GGA (PB86, PW91, PBE, RPBE) and hybrid (B3LYP, B3LYP*, PBE1PBE) functionals. This confirmation of the structural assumption underlying the estimation of Delta(E)0HL from experimental relaxation rate constants permits us to use this value to assess the ability of the density functionals for the calculation of the energy difference between the HS and LS states. Since the different functionals give values from -1000 to 12000 cm(-1), the comparison of the calculated values with the experimental estimate thus provides a stringent criterion for the performance of a given functional. Based on this comparison the RPBE and B3LYP* functionals give the best agreement with experiment.
在铁（II）低自旋配合物[Fe(bpy)₃]²⁺中，高自旋的⁵T₂g(t₄²g e²g)态与低自旋的¹A₁g(t₆²g)态之间的零点能量差ΔE₀HL估计在2500 - 5000 cm⁻¹范围内。该估计基于高自旋态光致布居后高自旋→低自旋弛豫的低温动力学，并且假设两种状态之间的键长差ΔrHL等于约0.2 Å的平均值，这是自旋交叉体系的实验结果。基于密度泛函理论（DFT）的计算验证了结构假设，因为发现低自旋态优化几何结构与配合物的实验X射线结构非常吻合，并且对于一系列常见广义梯度近似（GGA）（PB86、PW91、PBE、RPBE）和杂化（B3LYP、B3LYP*、PBE1PBE）泛函，预测的高自旋几何结构都彼此非常接近。从实验弛豫速率常数估计ΔE₀HL所依据的结构假设得到这一证实，使我们能够用该值评估密度泛函计算高自旋（HS）和低自旋（LS）态之间能量差的能力。由于不同泛函给出的值在 - 1000至12000 cm⁻¹之间，将计算值与实验估计值进行比较，从而为给定泛函的性能提供了一个严格的标准。基于这种比较，RPBE和B3LYP*泛函与实验结果吻合得最好。
