Orbital-Separation Approach for Consideration of Finite Electric Bias within Density-Functional Total-Energy Formalism
Orbital-Separation Approach for Consideration of Finite Electric Bias within Density-Functional Total-Energy Formalism
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考虑密度泛函总能量形式中的有限电偏置的轨道分离方法
DOI：
10.1103/physrevb.84.085120
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发表时间：
2011
影响因子：
3.7
通讯作者：
Seungwu Han
中科院分区：
文献类型：
--
作者：
Shusuke Kasamatsu;Satoshi Watanabe;Seungwu Han
我们提出了一种在密度泛函理论的Kohn-Sham形式下考虑偏置电压的简单方法。具体地说，考虑了偏压下金属-绝缘子-金属电容器的充电问题。这是通过将费米能级周围的Kohn-Sham轨道分离成阳极或阴极部分，并在确定占据数时应用不同的费米能级来实现的。详细讨论了本方法的形式基础。我们用不同介质厚度的Au-Vacuum-Au和Au-MgO-Au电容器对该方法进行了测试。结果表明，该方法可以准确地获得体介电常数和静态介电常数。我们还证明了界面对电容的影响可以直接研究。此外，我们将这种方法应用于石墨烯电容，并用电子动能对电容的贡献很好地解释了电容中的量子效应。本方法可以很容易地在传统的第一原理代码中实现，并提供了一种统一的方法来评估纳米器件的电容。
We present a simple approach for the consideration of bias voltage within the Kohn-Sham formalism of density-functional theory. To be specific, the electronic charging of a metal-insulator-metal capacitor under bias voltage is considered explicitly. This is achieved by separating the Kohn-Sham orbitals around the Fermi level into anode or cathode parts and applying different Fermi levels in the determination of occupation numbers. The formal basis of the present approach is discussed in detail. We test this method against Au-vacuum-Au and Au-MgO-Au capacitors with various dielectric thicknesses. It is shown that the bulk optical and static dielectric constants can be obtained accurately. We also demonstrate that interface effects on capacitance can be investigated straightforwardly. Furthermore, we apply this method to the graphene capacitor and identify the quantum effects in the capacitance, which is well explained by the contribution of the kinetic energy of electrons to the capacitance. The present method can be readily implemented in conventional first-principles codes and provides a unified approach to evaluate capacitance of nanodevices.