Structure of Glycine on Ge(100): Ab Initio Study of Its Scanning Tunneling Microscopy Images

We have performed ab initio calculations to study the atomic and electronic structure of glycine on the Ge(100) surface. Previously, adsorption configurations of glycine on Ge(100) was studied using scanning tunneling microscopy (STM), density functional theory (DFT) calculations, and high-resolution core-level photoemission spectroscopy (HRCLPES), where the most probable structure observed in experiment was assigned to an "intrarow O-H dissociated and N dative bonded structure". Using DFT calculations with van der Waals corrections, we find that the intrarow structure is less stable by about 0.23 eV than another structure called "interrow O-H dissociated and N dative bonded structure", different from the previous study. Furthermore, comparing the energetics and theoretical STM images with the experimental images for glycine on Ge(100), we conclude that the structure observed in the STM experiment is clearly identified as the interrow O-H dissociated and N dative bonded structure. Finally, these results for glycine on Ge(100) are compared with those on Si(100).