Computational Physics Approach to Scanning Tunneling Microscopy and Spectroscopy

Bardeen’s formula of the tunneling current is extended to include atomic features of the tip-surface system of scanning tunneling microscopy (STM). The electronic states of the sample surface and the tip is calculated by the local density functional approach (LDA) and they are used as the input data for the numerical simulation of the STM image. Normal images are resulted by the tip with a single apex atom, while abnormal images tend to be caused by the tip with several atoms on the tip apex. For the former type of the tips, tunnel current concentrates dominantly on a single apex atom. Some numerical results are presented, which demonstrate the importance of the first-principles simulation resolving puzzles appeared in STM process.