The structural and electronic properties of lead phthalocyanine (PbPc) adsorbed on graphene are studied theoretically using the van der Waals density functional method. It is revealed that an extended state analogous to an image potential state (IPS) emerges in a close-packed PbPc monolayer, hybridizing with the lowest IPS of graphene to form bonding and antibonding states at the PbPc–graphene interface. The impact of the PbPc adsorption manifests itself as increased effective masses of the hybrid IPSs as compared with those on pristine graphene. In particular, the bonding IPS exhibits a marked anisotropy in the effective mass, reflecting the uniaxially elongated unit cell adopted in the present calculations, whereas the antibonding one has an almost isotropic effective mass, which is comparable to experimental results obtained with two-photon photoemission spectroscopy of PbPc on highly oriented pyrolytic graphite and on single crystalline graphite. It is also shown that the increase in the effective masses is triggered by the hybridization with unoccupied molecular orbitals of PbPc that is localized at the Pb atom.

中文翻译：

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石墨烯铅酞菁覆盖层中具有大有效质量的杂化诱导图像势态

使用范德华密度泛函方法从理论上研究了吸附在石墨烯上的铅酞菁 (PbPc) 的结构和电子性质。结果表明，类似于图像势态 (IPS) 的扩展态出现在紧密堆积的 PbPc 单层中，与石墨烯的最低 IPS 杂化，在 PbPc-石墨烯界面形成键合和反键合状态。与原始石墨烯相比，PbPc 吸附的影响表现为混合 IPS 的有效质量增加。特别是，键合 IPS 在有效质量中表现出显着的各向异性，反映了本计算中采用的单轴细长晶胞，而反键的 IPS 具有几乎各向同性的有效质量，这与在高取向热解石墨和单晶石墨上用 PbPc 的双光子光电子能谱获得的实验结果相当。还表明，有效质量的增加是由与位于 Pb 原子上的 PbPc 的未占据分子轨道的杂交引发的。