Surface Science Research Centre and Department of Chemistry, University of Liverpool, Liverpool L69 3BX, UK.
J Phys Condens Matter. 2014 Apr 2;26(13):135003. doi: 10.1088/0953-8984/26/13/135003. Epub 2014 Mar 11.
A simplified density functional theory (DFT) method for investigating charged adsorbates on an ultrathin, insulating film supported by a metal substrate is developed and presented. This new method is based on a previous DFT development that uses a perfect conductor (PC) model to approximate the electrostatic response of the metal substrate, while the film and the adsorbate are both treated fully within DFT (Scivetti and Persson 2013 J. Phys.: Condens. Matter 25 355006). The missing interactions between the metal substrate and the insulating film in the PC approximation are modelled by a simple force field (FF). The parameters of the PC model and the force field are obtained from DFT calculations of the film and the substrate, here shown explicitly for a NaCl bilayer supported by a Cu(100) surface. In order to obtain some of these parameters and the polarizability of the force field, we have to include an external, uniformly charged plane in the DFT calculations, which has required the development of a periodic DFT formalism to include such a charged plane in the presence of a metal substrate. This extension and implementation should be of more general interest and applicable to other challenging problems, for instance, in electrochemistry. As illustrated for the gold atom on the NaCl bilayer supported by a Cu(100) surface, our new DFT-PC-FF method allows us to handle different charge states of adsorbates in a controlled and accurate manner with a considerable reduction of the computational time. In addition, it is now possible to calculate vertical transition and reorganization energies for the charging and discharging of adsorbates that cannot be obtained by current DFT methodologies that include the metal substrate. We find that the computed vertical transition energy for charging of the gold adatom is in good agreement with experiments.
发展并提出了一种用于研究负载于金属基底上的超薄绝缘膜上的带电吸附物的简化密度泛函理论（DFT）方法。该新方法基于之前的 DFT 发展，该发展使用完美导体（PC）模型来近似金属基底的静电响应，而薄膜和吸附物都在 DFT 中得到充分处理（Scivetti 和 Persson 2013 J. Phys.：Condens. Matter 25 355006）。在 PC 近似中，金属基底和绝缘膜之间缺失的相互作用通过简单的力场（FF）来建模。PC 模型和力场的参数是通过薄膜和基底的 DFT 计算获得的，此处明确显示了由 Cu(100)表面支撑的 NaCl 双层膜。为了获得这些参数中的一些以及力场的极化率，我们必须在 DFT 计算中包含一个外部均匀带电平面，这就要求我们开发一个周期性的 DFT 形式主义来包含这样一个带电平面在金属基底的存在。这种扩展和实现应该具有更普遍的意义，并且可应用于其他具有挑战性的问题，例如电化学。正如在由 Cu(100)表面支撑的 NaCl 双层膜上的金原子的情况所示，我们的新 DFT-PC-FF 方法允许我们以可控和准确的方式处理吸附物的不同电荷状态，同时大大减少计算时间。此外，现在可以计算充电和放电过程中吸附物的垂直跃迁和重组能，而这些能量是当前包含金属基底的 DFT 方法无法获得的。我们发现，计算得出的金吸附原子充电的垂直跃迁能与实验值吻合良好。
