I have been trying to simulate the extinction (absorption + scattering) spectra of colloidally synthesized metallic nanoparticles, i.e. particles that can freely move in an aqueous solution. I took inspiration from simulations of incoherent unpolarized dipoles (Incoherent unpolarized dipole) and simulated the metallic nanostructure in three orthogonal orientations and then averaged all the spectra. This gives good agreement with experimental spectra for low aspect ratio structures.
However, I am now trying to simulate an Ag nanowire with diameter of 50 nm and a length of 10 000 nm (see attached simulations), which seems to be more challenging. The experimental and simulated spectra do not match well, see below. This is mostly due to the contribution of the simulation where the source impinges on the side of the nanowire (labeled ‘sourcexaxis’ in the attachment), which gives the peak at 445 nm.
Surprisingly, when we define the averaged spectrum as (1 * the longitudinal spectrum + 2 * the transverse spectrum)/3, i.e. we double the weight of the ‘pol90’ simulation and we ignore the ‘sourcexaxis’ simulation, the agreement with the experiment is perfect. Of course, I don’t really have a physical reason to define the spectrum this way, but I’d be surprised if it is a coincidence.
My questions now are as follows:
- Would this method of averaging over three orthogonal orientations be the correct way of simulating the average behavior of a freely moving particle? If no, which method would you recommend?
- Can you think of any other reason why the averaged spectrum does not agree with experiment, whereas the spectrum with the strange weighing does match?
Thanks in advance!
AgNW_50nm_diameter_pentagonal_water_3D_singleP_pol0.fsp (340.7 KB) AgNW_50nm_diameter_pentagonal_water_3D_singleP_pol90.fsp (340.7 KB) AgNW_50nm_diameter_pentagonal_water_3D_singleP_pol90_sourcexaxis.fsp (343.3 KB)