silver nanosphere with diameter of 40nm at 420nm lambda

[Joshua]

Dear Dr. Yurkin,

I am new to ADDA.
I tried to obtain Qabs and Qext for silver nanosphere with diameter of
40nm at 420nm lambda using the following command line:
"adda -shape sphere -m 0.16687 2.1808 -lambda 0.42 -size 0.04"

I get my refrective index from http://refractiveindex.info

Am I doing this right? Or is there anything wrong with my command
line?

Regards,
Joshua

[Maxim Yurkin]

Dear Jochua,

Your question is too general. Overall, the command line looks fine. However, a number of issues may be relevant,
depending on details of your task. To name a few,

1) If your particles are in liquid, you should divide arguments of both "-lambda" and "-m" by the refractive index of
this liquid. See section 4 "Applicability of the DDA" of the manual.

2) The default accuracy (with given command line) may be not exactly satisfactory. See the same Section of the manual
and the discussion at http://groups.google.com/group/adda-discuss/browse_thread/thread/e078ffca3d205012 .

Moreover, it is always good to compare the DDA result with something. This can be reference simulations (e.g., the Miet
theory for spheres), simple experiment, etc. In your case (for spheres) the simplest way is to compare the output of
ADDA with any Mie code. Then you will immediately see if your command line is suitable.

Maxim.

[Slava Chushak]

I compared ADDA results with Mie calculations for Gold sphere from
http://iopscience.iop.org/0022-3727/41/18/185501

R = 26 nm
lambda=400 nm
m = 1.2540 + 1.4751i
Abs. cross-sect = 3677
Abs. efficiency = 1.731
(Abs. cross-sec / geom. cross-sect = 3677 / pi*R^2 = 1.732)

I used command:
adda -shape sphere -eq_rad 0.026 -lambda 0.40 -grid 64 -m 1.2540
1.4751

Got:
lambda: 0.4 Dipoles/lambda: 492.448
Required relative residual norm: 1e-05
Total number of occupied dipoles: 137376
...................................................
Cext = 0.002462697085
Qext = 1.159616611
Cabs = 0.002462695893
Qabs = 1.159616049

How to relate these results with Mie theory results?

Thanks.

[Maxim Yurkin]

The wavelength should also be scaled by refractive index of the medium (the refractive index is already scaled). So the
correct command line is

adda -shape sphere -eq_rad 0.026 -lambda 0.30 -grid 64 -m 1.2540 1.4751

The resulting CrossSec-Y is the following:
Cext = 0.004205145401
Qext = 1.980087802
Cabs = 0.003697132591
Qabs = 1.740878483

which is close enough to the Mie value. By the way, there are a lot of Mie codes at
http://www.scattport.org/index.php/programs-menu/mie-type-codes-menu , even online one -
http://zakharov.zzl.org/lstar.php .

There is another strange thing. If I just repeat the command line as you provided, I still get different results, in
particular Qabs=1.303432799. So please check your files once again (correspondence of the command line to the output).
If the discrepancy remains, please try the latest stable version of ADDA (1.0) and send the whole output of ADDA (at
least log and CrossSec-Y).

Maxim.