A Composite Energy Treatment for Sterically Hindered Cluster Models for the Si(100) Surface

Cluster models representing multiple dimer rows on the Si(100) surface suffer from unfavorable and unphysical steric interactions between hydrogen link atoms. A novel composite energy method is proposed to cancel such undesirable interactions present in the cluster model. In our composite method, the unphysical repulsive interaction energy between excised fragments (defined from the cluster model) is replaced by individual noninteracting fragments along with a Lennard-Jones-type repulsion term between the neighboring link atoms. The resulting composite energy and the associated gradients consist of well-defined individual subsystem calculations and can be used to perform geometry optimizations using such cluster models without additional constraints. Despite small differences from an ideal Si(100) reconstructed surface, this model can be used to investigate and analyze important surface chemical reactions. Results of allylic mercaptan adsorption on a Si(100) dimer using our proposed cluster model are reported to demonstrate the novel method's robustness.