Learning Forum

[navneetk]

Hi

I am struggling in deciding the boundary conditions for my structures. Considering a 3x3 Titanium Nanotube of certain length on glass substrate, I am not really sure of the boundary conditions and why do the minor changes in them affect the result so much. I got satisfactory result for Anti-Symmetric, Symmetric and PML (X,Y,Z respectively) boundary conditions (region was defined only for 1 nanotube) but when I coat these nanotubes with gold nanoparticles (in non-periodic way), I do not think I can use Anti-Symmetric or Symmetric boundary conditions anymore, right?

Is there any thumb-rule for the boundary conditions? And in my case, how should I proceed in case of nanotubes coated with nanoparticles? Any help is appreciated.

FYI- I am not able to attach my simulation file here as it does not supported the .fsp format

Thanks.

Navneet.

[Guilin Sun]

It seems this is a periodic structure. if so, you only need to simulate ONE unit cell, with periodic BCs in periodic directions. When the structure has symmetry, AND the source polarization has symmetry at the same time, then you can use symmetry BCs (Symmetric or Anti-Symmetric) in the periodic axes.
When the coating is not periodic, but has symmetry, you can only use Symmetric or Anti-Symmetric BCs in min side;
When the coating is not periodic, and has no symmetry, then no Symmetric or Anti-Symmetric BCs can be used.
Boundary conditions are important conditions to solve Maxwell Equations and other differential equations. They must be assigned correctly. Otherwise the result may be non-physical.
When the structure has symmetry, whether it is Symmetric or Anti-Symmetric BC depends on the source polarization. Please refer this page for more information Symmetric and anti-symmetric BCs in FDTD and MODE

[navneetk]

Hi gsun! Thanks for your answer.
You are right that periodic BCs should be used and only one cell is enough for simulation. But when I coat with Au nanoparticles, the structure is not periodic anymore as the Au particles are randomly coated on each nanotube. What should I do in that case as I am getting exact same result as without nanoparticles when I simulate one cell with symmetric BCs? Which implies the nanoparticles are not making any difference for the second result which seems wrong.
Thanks.

[Guilin Sun]

It seems this is a periodic structure. if so, you only need to simulate ONE unit cell, with periodic BCs. When the structure has symmetry, AND the source polarization has symmetry at the same time, then you can use symmetry BCs (Symmetric or Anti-Symmetric) in the periodic axes.
When the coating is not periodic, but has symmetry, you can only use Symmetric or Anti-Symmetric BCs in min side;
When the coating is not periodic, and has no symmetry, then no Symmetric or Anti-Symmetric BCs can be used.
Boundary conditions are important conditions to solve Maxwell Equations and other differential equations. When the structure has symmetry, whether it is Symmetric or Anti-Symmetric BCs