Pairing of hydrogen atoms on the Si(100)-(2×1) surface: The role of interactions among dimers

Local-density-functional calculations of the pairing of H atoms on the (100)-2×1 surface of Si are presented. We find that significant interactions between neighboring dimers along a row are present, favoring configurations where H-unpaired dimers are in the same row and have the H-atoms all on the same side. We discuss how these effects can contribute to the effective H-pairing energies determined experimentally.