Connected vacuum tail method and its application to scanning tunneling microscopy

Abstract A new improved method, the so-called connected vacuum tail (CVT) method, is proposed for the first-principles theoretical simulation of the STM/STS. The CVT method is especially powerful in reproducing the tail part of the surface electronic states extending far into vacuum. In this method, the natural asymptotic decay functions are used as the basis for the wave function in the far-vacuum tail. The expansion coefficients are obtained by solving the Schrodinger equation in the intermediate region by the Laue representation, and connecting these to the solutions of the wave function inside the surface obtained by the standard LDA method. The CVT method is utilized for the theoretical simulation of the STM/STS of Si(100) reconstructed surfaces. In this simulation, the dependence of the STM images on the tip-surface distance shows an interesting feature which corresponds well with experiment.