STM images of molecules on a metallic surface: a fast calculation based on a self-consistent semiempirical molecular orbital method

Abstract

We developed a new computational tool for analyzing observations obtained by a scanning tunneling microscope (STM). Our methods are based on self-consistent semiempirical molecular orbital method, which requires fewer computational resources than ab initio calculations, while maintaining an acceptable accuracy for comparison with submolecular-scale measurements. We calculated STM images for a bare graphite surface and naphthalene-l,4,5,8-tetracarboxylic dianhydride (NTCDA) molecules adsorbed on a graphite surface. Both of them concur with previously reported measurements. Regarding the graphite surface, dependence of bias voltage is reproduced. For NTCDA, we found that the brightness and shape of the calculated image depend on molecular orientation against the surface. That fact is consistent with experimental observations and structural models that have been described by other authors.