Atomic structure of the GaAs(001)-c(4x4) surface: first-principles evidence for diversity of heterodimer motifs

The GaAs(001)-c(4x4) surface was studied using ab initio atomistic thermodynamics based on density-functional theory calculations. We demonstrate that in a range of stoichiometries, between those of the conventional three As-dimer and the new three Ga-As-dimer models, there exists a diversity of atomic structures featuring Ga-As heterodimers. These results fully explain the experimental scanning tunneling microscopy images and are likely to be relevant also to the c(4x4)-reconstructed (001) surfaces of other III-V semiconductors.

Role of electronic correlation in the Si(100) reconstruction: a quantum Monte Carlo study

Recent low-temperature scanning tunneling experiments have questioned the generally accepted picture of buckled silicon dimers as the ground state reconstruction of the Si(100) surface, undermining the ability of density functional theory to accurately describe electronic correlations at surfaces. We present quantum Monte Carlo calculations on large cluster models of the surface, and conclude that buckling remains energetically favorable even when the present-day best treatment of electronic correlation is employed. The implications for experimental interpretation are discussed.