Departamento de Química Física, Universidad de Sevilla, c/Professor García González, s/n, E-41012 Sevilla, Spain.
J Chem Phys. 2011 Nov 21;135(19):194704. doi: 10.1063/1.3659141.
We present the evaluation of magnetic terms in a Cu(4)O(4) cubane-like system from truncated CI calculations, as a case study of polynuclear transition-metal complexes. We employ a new excitation selected configuration interaction (EXSCI) method based on the use of local orbitals. Taking advantage of the locality and then of the fact that the interactions vanish when the distance is large, the dimension of the CI is largely reduced. To the best of our knowledge these CI calculations are the largest one performed for polynuclear transition metal systems so far. The results show the presence of two leading ferromagnetic interactions between bridged Cu ions. Also the interactions between the unbridged Cu ions are ferromagnetic, but very weak, in contrast to the experimental data. The nature and amplitude of all the computed interactions are consistent with the relative orientation of the magnetic orbitals in the molecule, and correctly reproduce the susceptibility versus temperature curve. Our results indicate that it is possible to obtain similar fittings with sets of parameters representing different physical effects and put in evidence the drawbacks of the fitting based on oversimplified magnetic models. In this context, the presented computational strategy can be considered as a useful tool to help in the interpretation of the magnetic data and the validation of the magnetic interaction model in the polynuclear magnetic systems.
我们提出了在截断的组态相互作用（CI）计算中对 Cu(4)O(4)立方烷类似体系中的磁项进行评估，这是对多核过渡金属配合物的案例研究。我们采用了一种新的基于使用局域轨道的激发选择组态相互作用（EXSCI）方法。利用局域性，然后利用距离较大时相互作用消失的事实，大大降低了 CI 的维度。据我们所知，这些 CI 计算是迄今为止针对多核过渡金属体系进行的最大 CI 计算之一。结果表明，在桥接的 Cu 离子之间存在两个主要的铁磁相互作用。此外，未桥接的 Cu 离子之间的相互作用也是铁磁的，但非常弱，与实验数据相反。所有计算相互作用的性质和幅度都与分子中磁轨道的相对取向一致，并正确再现了磁化率随温度的变化曲线。我们的结果表明，有可能使用代表不同物理效应的参数集获得类似的拟合，并凸显基于过于简化的磁模型进行拟合的缺点。在这种情况下，所提出的计算策略可以被视为一种有用的工具，有助于解释磁数据和验证多核磁系统中的磁相互作用模型。
