Coupling Constants, High Spin, and Broken Symmetry States of Organic Radicals: an Assessment of the Molecules-in-Molecules Fragmentation-Based Method
Coupling Constants, High Spin, and Broken Symmetry States of Organic Radicals: an Assessment of the Molecules-in-Molecules Fragmentation-Based Method
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有机自由基的耦合常数、高自旋和破缺对称态：基于分子中碎片的方法的评估
DOI：
10.1021/acs.jctc.9b00563
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发表时间：
2019
影响因子：
5.5
通讯作者：
Raghavachari, Krishnan
中科院分区：
文献类型：
--
作者：
Sadhukhan, Tumpa;Beckett, Daniel;Thapa, Bishnu;Raghavachari, Krishnan
我们将我们的基于多层分子中分子(MIM)碎裂的方法扩展到开壳体系的研究，特别是有机自由基的研究。研究了一组有机单基、双基和多基，它们的大小范围很大，包含多达360个原子。用密度泛函理论(DFT)计算了MIM的总能量，并与完整的未碎裂能量进行了比较，以评估MIM的性能，并开发一种系统的方案来处理大的自由基体系。更具体地说，考虑了一个两层(MIM2)模型，该模型沿着主干包括共价键合的二聚体、三聚体或四聚体的碎裂方案，而较小基组的密度泛函作为理论的低水平。在高自旋态和几种可能的破坏对称(BS)态上对MIM方法进行了评估。当考虑相关的自旋-自旋相互作用时，总能量的误差小于1kcal·mol-1。此外，将MIM2的适用性扩展到预测位间磁交换耦合常数(J)，并与参考值进行了比较。此外，由于哈密顿对角化得到的能级在物理上更有意义，因此使用BS-DFT方法计算的J值被用来获得多自由基的较低自旋态能量。在大多数情况下，Full和MIM2计算的低自旋态总能量之差在1千卡·摩尔~(-1)以内。我们严格的量子化学研究表明，在BS-DFT的框架下，MIM可以成功地、可靠、准确地应用于大分子有机自由基的研究。
We extend the application of our multilayer molecules-in-molecules (MIM) fragmentation-based method to the study of open-shell systems, particularly organic radicals. A test set of organic mono-, di- and polyradicals with a wide range in size, containing up to 360 atoms, was investigated. Total energies computed with MIM using density functional theory (DFT) were compared with full, unfragmented energies to assess the performance of MIM and to develop a systematic protocol for the treatment of large radical systems. More specifically, a two-layer (MIM2) model with a fragmentation scheme along the backbone involving covalently bonded dimers, trimers, or tetramers was considered, with DFT at a smaller basis set serving as the low level of theory. The MIM method was evaluated on the high-spin state and several possible broken-symmetry (BS) states for di- and polyradicals. When relevant spin–spin interactions were considered, the errors in total energies were less than 1 kcal mol–1. In addition, the applicability of MIM2 was extended to predict the intersite magnetic exchange coupling constants (J), which were compared with reference values. Further, since the energy levels derived from Hamiltonian diagonalization are physically more meaningful, the calculatedJvalues estimated from the BS-DFT methodology were used to obtain the lower spin state energies of the polyradicals. The difference in calculated total energies of the lower spin state between full and MIM2 lie within 1 kcal mol–1in the majority of these cases. Our rigorous, quantum chemical study demonstrates that MIM can be successfully applied to the study of large organic radicals reliably and accurately within the framework of BS-DFT.