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首页> 外文期刊>The Journal of Chemical Physics >Electronic structure and spin coupling of the manganese dimer: The state of the art of ab initio approach
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Electronic structure and spin coupling of the manganese dimer: The state of the art of ab initio approach

机译：锰二聚体的电子结构和自旋耦合：从头算技术的最新发展

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A thorough ab initio study of the Mn2 dimer in its lowest electronic states that correlate to the ground Mn6S+Mn6S dissociation limit is reported. Performance of multireference methods is examined in calculations of the fully spin-polarized S=511+ u state against the recent accurate single-reference coupled cluster CCSDT results A. A. Buchachenko, Chem. Phys. Lett. 459, 73 2008. The detailed comparison reveals a serious disagreement between the multireference configuration interaction MRCI and related nonperturbative results on the one hand and the complete active space perturbation theory CASPT calculations on the other. A striking difference found in the CASPT results of the second and third orders indicates poor perturbation expansion convergence. It is shown that a similar problem has affected most of the previous calculations performed using CASPT2 and similar perturbative approximations. The composition of the active space in the reference multiconfigurational self-consistent field calculations, the core correlation contribution, and basis set saturation effects are also analyzed. The lower spin states, S=0–4, are investigated using the MRCI method. The results indicate a similar dispersion binding for all the spin states within the manifold related to the closed 4s shells, which appears to screen and suppress the spin coupling between the half-filled 3d atomic shells. On this premise, the full set of model potentials is built by combining the accurate reference CCSDT interaction potential for S=5 and the MRCI spin-exchange energies for the S5 states. This approach leads to the value of 550 cm-1 as a lower bound for the 1+ g ground-state dissociation energy. The spin-exchange energies themselves are found to comply with the simple Heisenberg model. The effective spin-coupling parameter J is estimated as -3.9 cm-1, a value roughly 2.5 times smaller in magnitude than those measured in the inert gas cryogenic matrices. Compressing of the Mn2 dimer in the matrix cage is suggested as the prime cause of this disagreement.
机译：据报道，在其最低电子状态下，与基态Mn6S + Mn6S离解极限相关的Mn2二聚体的从头开始进行了彻底的研究。针对最新精确的单参考耦合簇CCSDT结果A. A. Buchachenko，化学，在完全自旋极化S = 511 + u状态的计算中检查了多参考方法的性能。物理来吧参见459，732008。详细的比较揭示了一方面多参考配置交互作用MRCI与相关的非摄动结果之间存在严重分歧，另一方面，完整的主动空间摄动理论CASPT计算之间存在严重分歧。在二阶和三阶的CASPT结果中发现的惊人差异表明扰动扩展收敛性较差。结果表明，类似的问题影响了使用CASPT2和类似的扰动近似进行的大多数先前计算。还分析了参考多配置自洽场计算中活动空间的组成，核心相关贡献和基集饱和效应。使用MRCI方法研究了较低的自旋状态S = 0-4。结果表明，与封闭的4s壳有关的歧管内所有自旋状态具有相似的色散结合，似乎屏蔽并抑制了半填充3d原子壳之间的自旋耦合。在此前提下，通过将S = 5的准确参考CCSDT相互作用电势与S5态的MRCI自旋交换能相结合，可以建立完整的模型电势。这种方法导致550 cm-1的值作为1+ g基态解离能的下限。发现自旋交换能量本身符合简单的海森堡模型。有效的自旋耦合参数J估计为-3.9 cm-1，该值的大小大约是在惰性气体低温矩阵中测量的值的2.5倍。 Mn 2二聚体在基质笼中的压缩被认为是造成这种分歧的主要原因。

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