Scivetti Iván, Persson Mats
Surface Science Research Centre and Department of Chemistry, University of Liverpool, Liverpool, L69 3BX, United Kingdom. Daresbury Laboratory, Sc. Tech, Keckwick Lane, Daresbury, WA4 4AD, Warrington, United Kingdom.
J Phys Condens Matter. 2017 Sep 6;29(35):355002. doi: 10.1088/1361-648X/aa7c3a. Epub 2017 Jun 28.
We present calculations of vertical electron and hole attachment energies to the frontier orbitals of a pentacene molecule absorbed on multi-layer sodium chloride films supported by a copper substrate using a simplified density functional theory (DFT) method. The adsorbate and the film are treated fully within DFT, whereas the metal is treated implicitly by a perfect conductor model. We find that the computed energy gap between the highest and lowest unoccupied molecular orbitals-HOMO and LUMO -from the vertical attachment energies increases with the thickness of the insulating film, in agreement with experiments. This increase of the gap can be rationalised in a simple dielectric model with parameters determined from DFT calculations and is found to be dominated by the image interaction with the metal. We find, however, that this simplified model overestimates the downward shift of the energy gap in the limit of an infinitely thick film.
我们使用简化的密度泛函理论（DFT）方法，给出了吸附在铜衬底支撑的多层氯化钠薄膜上的并五苯分子前沿轨道的垂直电子和空穴附着能的计算结果。吸附质和薄膜在DFT中进行了完全处理，而金属则通过完美导体模型进行隐式处理。我们发现，根据垂直附着能计算得到的最高未占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）之间的能隙随着绝缘膜厚度的增加而增大，这与实验结果一致。在一个由DFT计算确定参数的简单介电模型中，可以解释这种能隙的增大，并且发现它主要由与金属的镜像相互作用主导。然而，我们发现这个简化模型在无限厚薄膜的极限情况下高估了能隙的向下移动。
