AI 中文总结
本文通过DFT+$U$研究Ag衬底上Fe-靛蓝配位聚合物，揭示其异构化与自旋交叉的相互作用，复现实验构型偏好，为该体系自旋态切换提供微观解释。
AI 中文摘要
自旋交叉（SCO）化合物为低维体系的可切换分子功能提供了途径，但一维（1D）SCO链因可研究除典型八面体场外的配体场，相关研究相对较少。本文采用第一性原理密度泛函理论（DFT+$U$），对实验合成于Ag(111)和Ag(100)衬底上的Fe-靛蓝配位聚合物链展开研究，该体系展现出配体场变化（异构化）与自旋交叉间的丰富相互作用。Ag(111)表面的异构化可使Fe中心的(N,O)螯合反式（trans）构型，与(N,N)-/(O,O)-螯合顺式（cis）构型相互转化；在0.66<U<3.00 eV区间内，Ag(111)上能量最低的反式和顺式解具有不同自旋构型。在参考值U=1 eV时，优选的反式解为混合LS-LS-HS构型，顺式解为LS-LS-LS构型；在0.88<U<3.75 eV区间内，可复现实验观测到的Ag(111)上顺式链占优、Ag(100)上反式链占优的结果。为解释这些结果，采用了简化模型与自旋分辨的Fe 3d投影态密度，而悬空链计算揭示了应变敏感的LS-HS竞争。这些结果为一维配位聚合物中异构化控制的自旋态切换提供了微观解释。
英文摘要
Spin-crossover (SCO) compounds offer a route to switchable molecular functionality in reduced dimensions. However, one-dimensional (1D) SCO chains, which offer the possibility to study ligand fields other than the paradigmatic octahedral field, remain comparatively little studied. Here, we use first-principles density functional theory (DFT+$U$) to investigate Fe-indigo coordination-polymer chains synthesized experimentally on Ag(111) and Ag(100) substrates. These display a rich interplay between changes in ligand field (isomerization) and spin crossover. On-surface isomerization on Ag(111) interconverts (N,O)-chelated \textit{trans} configuration and (N,N)-/(O,O)-chelated \textit{cis} configurations at the Fe centers. The lowest-energy \textit{trans} and \textit{cis} solutions on Ag(111) have different spin configurations over the interval $0.66<U<3.00$~eV. At the reference value $U=1$~eV, the preferred \textit{trans} solution is the mixed LS--LS--HS configuration, whereas the preferred \textit{cis} solution is LS--LS--LS. The experimentally observed preference for \textit{cis} chains on Ag(111) and \textit{trans} chains on Ag(100) is reproduced for the range $0.88<U<3.75$~eV. To interpret these results, toy models and spin-resolved Fe $3d$ projected densities of states are used, while freestanding-chain calculations reveal a strain-sensitive LS--HS competition. These results provide a microscopic explanation for isomerization-controlled spin-state switching in a 1D coordination polymer.
