Modeling steps and kinks on the surface of calcite.
This work presents modeling results on the cleavage face of calcite as well as on steps and isolated kinks on this face. We used static lattice energy minimization and interatomic potentials fitted to bulk properties. The energy needed to cleave a bulk calcite crystal along the [1 0 (-)1 4] plane was calculated to be 0.59 J m(-2) in agreement with previous studies using the same potentials. The perfect surface reconstructs in the top few atomic layers, but its symmetry corresponds to the bulk termination. By contrast, the (1 0 (-)1 4) surface with cleavage steps present reconstructs to form a (2 x 1) super cell. This may help explain experimental observations of (2 x 1) symmetry on calcite surfaces. The energy required to form a monatomic obtuse step is calculated to be 1.3 x 10(-10) J m(-1) and for the acute step, 2.4 x 10(-10) J m(-1), suggesting that obtuse steps dominate on cleaved surfaces. Along the two types of steps, a total of 16 kink geometries exist. We calculated kink defect energy with two different approaches: one where kink pairs were added onto infinitely long steps and one where kinks were placed inside pits on a cleavage surface. Calculations on infinitely long steps show that for vacuum conditions, kink pairs possess roughly identical formation energy, about 1.2-2.2 eV, so based on energetics one cannot expect significant differences in kink site frequency
Kristensen
Rune
R
Geological Institute, University of Copenhagen, Oster Voldgade 10, Copenhagen K, Denmark. runek@fys.ku.dk
Stipp
S L S
SL
Refson
Keith
K