Wang Yu, Li Xiaoguang
Institute for Advanced Study, Shenzhen University, Shenzhen 518060, China.
Phys Chem Chem Phys. 2022 Sep 14;24(35):21122-21130. doi: 10.1039/d2cp02793c.
Recent scanning tunneling spectroscopy with single metallocene molecule-functionalized tips have proved to be a powerful tool to probe and control individual spins and spin-spin exchange interactions due to the robustness of the magnetic properties of the metallocene molecule in different surroundings. However, accurate prediction of such robustness at a first-principles-based level by the conventional density functional theory (DFT) has remained challenging. In this paper, we have performed a detailed investigation of the evolution of electronic and magnetic properties of a nickelocene molecule (NiCp) in different environments, , free-standing, adsorbed on Cu(100) and as a functionalized tip apex. Using an embedding method, which combines DFT and the complete active space self-consistent field (CASSCF) method recently developed, we demonstrate that the nickelocene molecule almost preserves its spin and magnetic anisotropy upon adsorption on Cu(100), and also in the position of the tip apex. In particular, the cyclic π* orbital of the Cp rings could hybridize with the singly occupied d orbitals of the Ni center of the molecule, protecting these orbitals from external states. Hence the molecular spin maintains = 1, the same as in the free-standing case, and its magnetic anisotropy is also robust with energies of 3.56, 3.34, and 3.51 meV in free-standing, adsorbed on Cu(100), and functionalized tip apex states, respectively, in good agreement with previous theoretical and experimental results. This work thus provides a first-principles-based understanding of the relevant experiments. Such agreement between theoretical simulations and experimental measurements highlights the potential usefulness of the method for investigating the local electronic and spin states of organometallic molecule-surface composite systems.
最近，使用单茂金属分子功能化尖端的扫描隧道光谱已被证明是一种强大的工具，可用于探测和控制单个自旋以及自旋-自旋交换相互作用，这是由于茂金属分子在不同环境中的磁性能具有稳健性。然而，通过传统密度泛函理论（DFT）在基于第一性原理的层面上准确预测这种稳健性仍然具有挑战性。在本文中，我们对二茂镍分子（NiCp）在不同环境（即自由状态、吸附在Cu(100)上以及作为功能化尖端顶点）下的电子和磁性能演变进行了详细研究。使用一种结合了DFT和最近开发的完全活性空间自洽场（CASSCF）方法的嵌入方法，我们证明二茂镍分子在吸附在Cu(100)上以及处于尖端顶点位置时几乎保留了其自旋和磁各向异性。特别是，Cp环的环状π*轨道可以与分子中Ni中心的单占据d轨道杂化，从而保护这些轨道免受外部状态的影响。因此，分子自旋保持S = 1，与自由状态下相同，并且其磁各向异性也很稳健，在自由状态、吸附在Cu(100)上以及功能化尖端顶点状态下的能量分别为3.56、3.34和3.51 meV，与先前的理论和实验结果吻合良好。这项工作因此提供了基于第一性原理的对相关实验的理解。理论模拟与实验测量之间的这种一致性突出了该方法在研究有机金属分子-表面复合系统的局部电子和自旋状态方面的潜在有用性。
