Chemistry Reference
In-Depth Information
Figure 15
Two possible simulation cells for FP-GFBC: (a) vacuum region isolates the
dislocation from its periodic images, while (b) region 3 is expanded up to the boundaries
of the simulational cell. In the direction of the dislocation line, the cell is one periodic
length thick.
FP-GFBC method), but it uses a classical potential to relax the environment
around the region of interest, instead of a Green's function solution. As
with the FP-GFBC, the QuASI region of interest is modeled using DFT. This
method was especially developed to investigate critical regions in the neighbor-
hood of dislocations, but not necessarily at the dislocation cores. This genera-
lity is achieved by allowing complete freedom in the placement of the quantum
cluster(s) inside the classical environment [Figure 16(a)]. Such a freedom
allows the detailed modeling of phenomena that are affected by the presence
of nearby dislocation(s) but are spatially located outside the dislocation cores.
As an example, the methodology has been used to investigate the formation of
vacancies as a function of their distance from an edge dislocation. As with the
GFBC and FP-GFBC methods, this methodology also makes use of an iterative
approach.
Figure 16
(a) Example of simulation cell: The gray parallelepiped constitutes the
classical cell inside which is the critical region (spherical region marked DFT). (b)
Schematic 2D representation of the shell structure. Shells 1, 2, and 3 correspond to the
critical region, i.e., are considered in the DFT calculation. During the classical relaxation
all shells are considered, but only atoms in shells 2, 3, and 4 are allowed to move.
