Department of Chemistry, University of North Bengal, Siliguri 734013, West Bengal, India.
J Phys Chem A. 2010 Jun 24;114(24):6641-7. doi: 10.1021/jp1013835.
Nonequivalent magnetic interactions in systems with multiple magnetic centers can be explored through a proper description of exchange coupling. The magnetic exchange coupling constant (J) in systems with two magnetic sites is reliably estimated using Heisenberg-Dirac-van Vleck (HDVV) model through broken symmetry approach (BS) within a density functional theory (DFT) framework. However, in case of systems with multiple magnetic centers, exchange coupling constants, evaluated through state-of-the-art techniques, are often found to be inadequate to produce a correct fingerprint of the nature of magnetic interactions therein. This work suggests a new scheme to estimate exchange coupling constants in such systems. In this strategy, distribution of spins on magnetic sites in the ground state of systems with multiple magnetic centers is computed. On the basis of this spin mapping, exchange coupling constants between specific pairs are estimated through BS-DFT approach while keeping all other paramagnetic atoms magnetically inactive. Nonetheless, the effect of magnetically inert paramagnetic sites is already taken into account by the process of spin mapping, which is further justified through expressing the HDVV Hamiltonian in terms of spin density operators. We employ this technique to hypothetical benchmark systems, H(3)He(3) and H(4)He(4) followed by real molecules, cationic manganese trimer, 1,3,5-benzenetriyltris (N-tert-butyl nitroxide), and a pentanuclear manganese complex. Results are found to be concordant with the already established nature of magnetic interaction in these systems. This strategy is different from the most popular scheme to compute J in systems with multiple magnetic centers in the sense that it avoids the formation of a large matrix out of different spin configurations and thus provides a reliable and computationally economic way to address the magnetic interactions in non isotropic systems with multiple magnetic sites.
在具有多个磁中心的系统中，通过对交换耦合的适当描述可以探索不等效的磁相互作用。在密度泛函理论（DFT）框架内，通过破缺对称性方法（BS），可以使用海森堡-狄拉克-范弗莱克（HDVV）模型可靠地估计具有两个磁位的系统中的磁交换耦合常数（J）。然而，在具有多个磁中心的系统中，通过最先进的技术评估的交换耦合常数往往不足以产生其中磁相互作用的正确特征。本工作提出了一种估计此类系统中交换耦合常数的新方案。在此策略中，计算了具有多个磁中心的系统基态中磁位上的自旋分布。在此自旋映射的基础上，通过 BS-DFT 方法估计特定对之间的交换耦合常数，同时使所有其他顺磁原子磁惰性。尽管如此，通过自旋映射过程已经考虑了顺磁惰性顺磁位的影响，这进一步通过将 HDVV 哈密顿量表示为自旋密度算子来证明。我们将此技术应用于假设的基准系统 H(3)He(3)和 H(4)He(4)，然后是实际分子，阳离子锰三聚体 1,3,5-苯三基三（N-叔丁基氮氧化物）和五核锰络合物。结果与这些系统中已经确立的磁相互作用性质一致。与在具有多个磁中心的系统中计算 J 的最流行方案不同，该策略避免了从不同自旋构型形成大矩阵，因此为解决具有多个磁位的非各向同性系统中的磁相互作用提供了可靠且计算经济的方法。
