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Dielectric constant calculation of Si-NC

Si-NC in Vacuum

An atom-centered Si-NC (Si211H140) was placed in the corner of a simple cubic box (80 a.u.). Self-consistent electron relaxation cycle was performed to find the minimized total energy and then the process was repeated after adding a point charge in the center of the box.

Dump files of electron density and potencials are no longer available in blafis due to its large size (~40GB per file). They are still available upon request.

After fiddling with the code, I got the following result using these conditions

SiNC.dump
SiNCpc.dump
1.0                           ! Localized charge [...,-2,-1,+1,+2,...]
0.0 0.0 0.0                   ! Averaging stencil diameters along X, Y and Z [Bohr]
1                             ! nspin [1 - Spin average, 2 - Spin polarized]
450 450 450                   ! Grid [nga, ngb, ngc]
 80.000     0.000     0.000   ! a1 lattice vector [Bohr]
  0.000    80.000     0.000   ! a2 lattice vector [Bohr]
  0.000     0.000    80.000   ! a3 lattice vector [Bohr]
0.0 0.0 0.0                   ! Center of symmetry sphere/slab (z-coord) [Bohr]
20.000                        ! Cut-off radius/half-width sphere/slab [Bohr]
200                           ! Number of bins for plot

Note that the stencil diameter is zero, ie, no local averaging is carried out. The source code can be found at blafis:/home/coutinho/aimpro/screening/devel/screen.f90

Stencil diameter dependency

Now we need to make a few tests, namely, increase the stencil diameter and produce (1) a plot with local rho functions vs radius for several stencil diameters, and (2) a plot with cumulative rho functions vs radius for several stencil diameters. Use stencil diameters of D = (0, 1, 5, 10, 20) atomic units. Mind that the stencil diameters are directly set at the input files (and not its radii as in some input file comments suggest).
Results are pictured below.
Calculations with stencil diameters of D= (30, 40) were abandoned due to high computational costs.

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Size effects

Tests with smaller and larger SI-NCs are in progress …

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Surface modification

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Data available in the following files:
blafis:~tiago/queue/sinc/radial.Si377.*.norm.dat.d0 (normalized)
blafis:~tiago/queue/sinc/nc-sc.Si377.H196/scr/radial.dat.d0 (un-normalized charge density for -H)
blafis:~tiago/queue/sinc/nc-sc.Si377.F196/scr/radial.dat.d0 (un-normalized charge density for -F)

The same atom-centered Si-NC passivated with hydrogen was also passivated with Fluorine (Si211F140) and -OH (Si211O100H80) and placed in the same simple cubic box (80 a.u.). After structural relaxation, self-consistent electron relaxation cycle was performed to find the minimized total energy and then the process was repeated after adding a point charge in the center of the box. The following plots sumarize the obtained results.

H passivation

F passivation

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OH passivation

Summary

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Medium (host) effects

Calculations for SiNC embeded in diferent mediums are on hold!