Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain.
J Chem Phys. 2010 Oct 21;133(15):154701. doi: 10.1063/1.3502682.
The adsorption of phthalocyanines (Pc) to various surfaces has recently been reported to lead to a lowering of symmetry from C4 to C2 in scanning tunneling microscope (STM) images. Possible origins of the reduced symmetry involve the electronic structure or geometric deformation of the molecules. Here, the origin of the reduction is clarified from a comprehensive theoretical study of CoPc adsorbed on the Cu(111) surface along with the experimental STM data. Total energy calculations using different schemes for the exchange-correlation energy and STM simulations are compared against experimental data. We find that the symmetry reduction is only reproduced when van der Waals corrections are included into the formalism. It is caused by a deformation along the two perpendicular molecular axes, one of them coming closer to the surface by around 0.2 Å. An electronic structure analysis reveals (i) the relevance of the CoPc interaction with the Cu(111) surface state and (ii) that intramolecular features in dI/dV maps clearly discriminate a Co-derived state from the rest of the Pc states.
酞菁（Pc）在各种表面上的吸附最近被报道会导致在扫描隧道显微镜（STM）图像中从 C4 对称降低到 C2。对称性降低的可能原因涉及分子的电子结构或几何变形。在这里，我们通过对吸附在 Cu(111)表面上的 CoPc 的综合理论研究以及实验 STM 数据，澄清了这种对称性降低的起源。使用不同的交换相关能量方案和 STM 模拟进行总能量计算，并与实验数据进行比较。我们发现，只有当形式理论中包含范德华修正时，才会重现对称性降低。这是由沿着两个垂直分子轴的变形引起的，其中一个分子轴大约向表面靠近 0.2 Å。电子结构分析揭示了 (i) CoPc 与 Cu(111)表面态相互作用的相关性，以及 (ii) 在 dI/dV 图谱中，分子内特征可以清楚地区分 Co 衍生态与其余 Pc 态。
