Particle in an octopus
Octopus can actually run 2D systems where the shape of the simulation box is defined by what is white in an image file. Here is an example of a “particle in an octopus”, in which we have a constant potential and an octopus-shaped quantum dot. To run it, you will need to have built the code with the optional library GDLIB.
For this example we will need two files:
CalculationMode = gs FromScratch = yes Dimensions = 2 %Species "null" | species_user_defined | potential_formula | "0" | valence | 1 % %Coordinates "null" | 0 | 0 % BoxShape = box_image BoxShapeImage = "gdlib.png" ff = 20 %Lsize 135 / ff | 95 / ff % TheoryLevel = independent_particles ConvEigenError = yes %Output wfs | plane_z %
Make this file available in the run directory. You can download it by clicking on the image bellow. It is also available in the PREFIX/share/octopus directory from your Octopus installation.
The wavefunction are obtained by using:
%Output wfs % OutputFormat = plane_z
View it in
plot 'static/wf-st0001.z=0' u 1:2:3 linetype palette
splot 'static/wf-st0001.z=0' u 1:2:(0):($3*500) with pm3d
Where does the wavefunction localize, and why?
- See how the total energy scales with the size of the system (controlled by the
ffparameter in the input file). How does it compare to the formula for a particle in a box?
- Look at the wavefunctions of the unoccupied states.
- Think of a serious application that would use the ability to define the simulation box by an image!