First-principles estimate of Peierls energy in sodium chloride

Resumo

The Peierls barrier height for edge dislocations in sodium chloride crystal has been estimated from first principles based on the density functional theory. The calculation was performed using a plane-wave expansion of the Bloch functions of a periodic structure with sp. gr. Pmmm and a supercell containing an edge dislocation dipole of dominating slip system \({1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}\langle 110\rangle \{ \overline 1 10\} \). It is shown within the generalized gradient approximation for the exchange-correlation energy that, among the two symmetric positions of dislocation line in the Peierls relief, configuration I, which has a compact core of size d ≈ b (b is the Burgers vector length), is characterized by minimum energy. The second symmetric position corresponds to configuration II with an extended core (d ≈ 2b). Its energy exceeds the Peierls relief minimum by 1.2 × 10^–2 eV (per lattice period). An application of compressive stress changes the form of crystalline relief: its minimum moves to position II.