Gallium adatoms on GaN polar surfaces - thermodynamic data from DFT calculations.

These data come from density functional theory (DFT) calculations using the SIESTA code. The polar surfaces of gallium nitride (GaN) were represented by a slab model with a lateral size of 2a*sqrt(3)x2a*sqrt(3). The number of gallium adatoms on the surfaces was systematically increased, starting from a clean surface and progressing to a metallic bilayer. First principles phonon calculations was performed to determine vibrational free energies for the surfaces. The chemical potential of Ga adatoms was calculated as the derivative of the free energy over the number of adatoms, using systems with the lowest free energy at a given temperature.

There are two main catalogs separately for GaN(000-1) and GaN(0001) polar surfaces. The names of the subdirectories indicate the number of Ga adatoms on the polar GaN surfaces containing 12 surface sites. There are several alternative atomic configurations in each directory.

The relaxed geometries of the systems are in the "structure.xsf" files, and the determined total energy is in the "DFT_energy.txt" files.

The "free_energy.txt" files contain the basic thermodynamic properties (vibrational entropy, specific heat, thermal energy, vibrational free energy) determined for the part of the system containing the 3 Ga-N layers closest to the surface and adatoms placed on the surface. It is possible to use and compare the relative differences in these parameters within systems representing the surface.

Changes in the chemical potential of Ga adatoms on GaN polar surfaces as a function of temperature and surface coverage are placed in the files "chemical_potential_Ga_adatoms_GaN_000-1.txt" and "chemical_potential_Ga_adatoms_GaN_0001.txt", respectively.

Basic units are electron-volt (eV) for energy, Kelvin(K) for temperature and Angstrom (Ang) for length.

For specification of XSF file format see http://www.xcrysden.org/doc/XSF.html