金屬電極的電子結構自洽運算

Abstract

本研究在基本密度泛函理論的架構下，發展出一套以第一原理計算金屬-真空-金屬奈米接面系統電子結構的方法。接面系統中金屬的原子核正電荷以凝膠模型近似，在要求系統電中性的束制下，自洽去解算等效單電子系統的耦合帕松方程式與薛丁格方程式，交換相關能泛函採用局域密度近似。論文中研究了威格納半徑為2至6的金屬電極，分別計算左右為相同金屬及不同金屬的接面，並比較真空層寬度與外加偏壓對系統電子結構的影響。計算所得之電子密度和位能都有顯著的夫里德耳振盪，此振盪大幅增加計算收斂難度。對系統施以外加偏壓時，在兩個表面間有電荷轉移的現象發生。在不同金屬組成的接面系統中，左右電極存在一內在感應電位差。

Within the framework of density-functional theory (DFT), the electronic structure of bimetal junctions is calculated by a first-principles method. The positive charges of metals are modeled as a uniform positive background (Jellium model). The method solves the coupled Poisson and Schrödinger equations iteratively with the constraints of the charge neutrality. The exchange-correlation functional of the effective single-particle system is approximated by the local density approximation (LDA). The self-consistent electron structures are obtained for identical and dissimilar contacts with rs=2-6. Junctions with different separations and external biases are compared. There exist substantial Friedel oscillations in densities and potential energies. Charge transfer between two electrodes occurs when an external bias is applied. An intrinsic voltage difference is generated by the contact of dissimilar metals.