Circular dichroism for a fingers crossed dimer of gold nanorods • terms

Objective

This example illustrates the calculation of far-field spectra for a dimer of particles described by external T-matrix files. The structure consists of two prolate gold spheroids in water, oriented in a chiral “fingers crossed” configuration that yields strong optical activity.

This simulation uses the following input file

ModeAndScheme 2 3 
MultipoleCutoff 5
Wavelength 400 800 200
Medium 1.7689 # careful: be consistent with external T-matrix

TmatrixFiles 1
"tmat_Au20x50_Nmax4.tmat" 

OutputFormat HDF5 cross_sections

# dimer, dihedral pi/4
Scatterers 2
TF1 0 -50 0.0 50 0.0 0.0 0.0  2.5
TF1 0  50 0.0 50 0.0 0.7853982 0  2.5

The T-matrix file was previously created with SMARTIES using these parameters

head -n14 smarties.m

clearvars

wavelength = 400:2:800;
epsilon=epsAu(wavelength);
medium=1.33;

% stParams.a=20; stParams.c=50;
stParams.a=10; stParams.c=20;
stParams.N=4; stParams.nNbTheta=40;

stOptions.bGetR = false;
stOptions.Delta = 0;
stOptions.NB = 0;
stOptions.bGetSymmetricT = false;

The command to run the example is simply

../../build/terms input > log

The full log contains basic details of the calculations, and finishes with the timing.

Show log file (click to open)

readInputFile> Parsing file input

readInputFile> Detected keyword ModeAndScheme
               mode=2 => spectrum_FF for far-field quantities
               scheme=3 => Seek T^(j) using Mackowski's approach
readInputFile> Detected keyword MultipoleCutoff
               Supplied ncut(1)=  5
               Setting ncut(2)= ncut(1)
               Setting ncut(3)=  -8
readInputFile> Detected keyword Wavelength
               Wavelength LB (nm):   400.000000
               Wavelength UB (nm):   800.000000
               nsteps, step:       200    2.0000
readInputFile> Detected keyword Medium
               Constant host epsilon=  1.7689E+0
readInputFile> Detected keyword TmatrixFiles
readInputFile> Detected keyword OutputFormat
               OutputFormat=HDF5
               All output files are stored in file "cross_sections.h5                                               "

readInputFile> Detected keyword Scatterers
 with nscat=    2

readInputFile> Descriptor(s) and circumscribing sphere(s):

 scatID String                  x          y          z         R_0
    1   TF1                 0.0000E+0 -5.0000E+1  0.0000E+0  5.0000E+1
    2   TF1                 0.0000E+0  5.0000E+1  0.0000E+0  5.0000E+1

readInputFile> Individual geometry characteristic(s):

 scatID Details
    1   Euler angles:  0.0000000  0.0000000  0.0000000 asp. ratio:  2.5000000
    2   Euler angles:  0.0000000  0.7853982  0.0000000 asp. ratio:  2.5000000

readInputFile> Finished parsing  7 keywords


spectrumFF> ===== Wavelength:   400.00 (nm) ======================

solve> Prestaging...
solve> Staging and solving/inverting...
solve> Done!


diagnoseTmat> WARNING: Tr(Tmat) not converged to 1.0E-08 for n <= nmax=  5


diagnoseTmat> WARNING: Max(|SymErr(Tmat)|)/Max(|Tmat|)= 5.7E-04

calcOAprops> <csExt>=  8.92356552E+03 nConv=  0
             <csSca>=  1.28057254E+03 nConv=  0
             <csAbs>=  7.64299298E+03

             <cdExt>=  1.59634366E+02
             <cdSca>=  9.09944193E+01
             <cdAbs>=  6.86399471E+01

calcCs> csExt=  8.11985185E+03 nConv=  0
         csSca=  1.11248256E+03 nConv=  0
         csAbs=  7.00736929E+03

...
termsProgram> Program run time (CPU & real in s):  1.049E+00  8.280E-01

Orientation-averaged results

Rows: 3,618
Columns: 5
$ wavelength <dbl> 400, 400, 400, 400, 400, 400, 402, 402, 402, 402, 402, 402,…
$ crosstype  <chr> "Abs", "Abs", "Abs", "Abs", "Abs", "Abs", "Abs", "Abs", "Ab…
$ variable   <chr> "total", "I1", "I2", "I3", "I4", "I5", "total", "I1", "I2",…
$ dichroism  <dbl> 6.863995e+01, 6.016556e+01, 9.546410e+00, -1.094083e+00, 2.…
$ average    <dbl> 7642.9929773, 5955.4637817, 1558.6333188, 123.3448785, 5.41…

This chiral dimer produces strong circular dichroism.

Last run: 05 December, 2023