Relaxation of the ZnTe and CuCl (110) surfaces

Abstract

Ab initio molecular dynamics simulations of the ZnTe and CuCl (110) surfaces are employed to study surface atomic relaxation. We believe that these are the first such computations for heteropolar semiconductors, and for their surfaces in particular. The molecular dynamics follows the Sankey–Niklewski method, and electrostatic interactions are incorporated using Ewald’s scheme for Gaussian atomic charge distributions. Hence the electrons are treated in the local-density approximation, forces are computed using the Hellmann–Feynman method, and atoms move to equilibrium according to Newton’s laws. Using ‘‘dynamical quenching,’’ we allow the ‘‘ideal’’ surfaces to relax according to these laws of physics and then address a controversy concerning whether Coulomb forces can play a significant role in determining the (110) zinc blende surface relaxation: Coulomb effects are not negligible for ZnTe (110) and are as dominant as covalent effects for CuCl (110). They reduce the (almost rigid) bond rotation angle ω1 due to movement of the anions up out of the (110) surface by about 6° for ZnTe, and cause the CuCl anion rotation angle to be nearly zero.