Dear DDSCAT community,

Hello, I am new and learning to use DDSCAT 7.3. I am at first trying to reproduce results from Dr. Flatauâ€™s 2-spheres model that are in contact with each other (APPLIED OPTICS / Vol. 32, No. 18 / 20 June 1993 ). I have tried to reproduce the data, but with no luck. First of all, my S11 and S22 values are the same. Also, when I plot and compare the points to the literature values, the forward scattering looks like it reproduces S11, whereas the backscattering looks more like S22 character. Please let me know if you have suggestions for me.

Here is my input file, and header of my shape.dat file.

Thank you,

Yohanna White

*

shape.dat:

>TARELL ellipsoidal grain; AX,AY,AZ= 32.0000 32.0000 32.0000

34512 = NAT

1.000000 0.000000 0.000000 = A_1 vector

0.000000 1.000000 0.000000 = A_2 vector

1.000000 1.000000 1.000000 = lattice spacings (d_x,d_y,d_z)/d

-15.50000 0.50000 0.50000 = lattice offset x0(1-3) = (x_TF,y_TF,z_TF)/d for dipole 0 0 0

JA IX IY IZ ICOMP(x,y,z)

1 -2 -4 -16 1 1 1

2 -1 -4 -16 1 1 1

3 0 -4 -16 1 1 1

4 1 -4 -16 1 1 1

5 -3 -3 -16 1 1 1

ddscat.par:

' ========== Parameter file for v7.3 ==================='

' Preliminaries '

'NOTORQ' = CMTORQ*6 (DOTORQ, NOTORQ) — either do or skip torque calculations

'PBCGS2' = CMDSOL*6 (PBCGS2, PBCGST, GPBICG, QMRCCG, PETRKP) — CCG method

'FFTMKL' = CMETHD*6 (GPFAFT, FFTMKL) — FFT method

'GKDLDR' = CALPHA*6 (GKDLDR, LATTDR, FLTRCD) — DDA method

'NOTBIN' = CBINFLAG (ALLBIN, ORIBIN, NOTBIN)

' Initial Memory Allocation '

100 100 100 = dimensioning allowance for target generation

' Target Geometry and Composition '

'FROM_FILE' = CSHAPE*9 shape directive

no SHPAR parameters needed

2 = NCOMP = number of dielectric materials

'm1.33_0.001' = name of file containing RI info

'm1.33_0.001' = name of file containing RI info

' Additional Nearfield calculation? '

0 = NRFLD (=0 to skip nearfield calc., =1 to calculate nearfield E)

0.0 0.0 0.0 0.0 0.0 0.0 (fract. extens. of calc. vol. in -x,+x,-y,+y,-z,+z)

' Error tolerance '

1.00e-5 = TOL = MAX ALLOWED (NORM OF |G>=AC|E>-ACA|X>)/(NORM OF AC|E>)

' maximum number of iterations allowed '

300 = MXITER

' Interaction cutoff parameter for PBC calculations '

1.00e-5 = GAMMA (1e-2 is normal, 3e-3 for greater accuracy)

' Angular resolution for calculation of <cos>, etc. '

0.5 = ETASCA (number of angles is proportional to [(3+x)/ETASCA]^2 )

' Wavelengths (micron) '

6.283 6.2833 1 'LIN' = wavelengths (first, last, how many, how=LIN,INV,LOG,TAB)

' Refractive index of ambient medium'

1.000 = NAMBIENT

' Effective Radii (micron) '

10.000 10.000 1 'LIN' = eff. radii (first, last, how many, how=LIN,INV,LOG)

' Define Incident Polarizations '

(0,0) (1.,0.) (0.,0.) = Polarization state e01 (k along x axis)

2 = IORTH (=1 to do only pol. state e01; =2 to also do orth. pol. state)

' Specify which output files to write '

0 = IWRKSC (=0 to suppress, =1 to write ".sca" file for each target orient.

' Specify Target Rotations '

0. 0. 1 = BETAMI, BETAMX, NBETA (beta=rotation around a1)

0. 0. 1 = THETMI, THET MX, NTHETA (theta=angle between a1 and k)

0. 0. 1 = PHIMIN, PHIMAX, NPHI (phi=rotation angle of a1 around k)

' Specify first IWAV, IRAD, IORI (normally 0 0 0) '

0 0 0 = first IWAV, first IRAD, first IORI (0 0 0 to begin fresh)

' Select Elements of S_ij Matrix to Print '

2 = NSMELTS = number of elements of S_ij to print (not more than 9)

11 22 = indices ij of elements to print

' Specify Scattered Directions '

'LFRAME' = CMDFRM (LFRAME, TFRAME for Lab Frame or Target Frame)

2 = NPLANES = number of scattering planes

0. 0. 180. 5 = phi, thetan_min, thetan_max, dtheta (in degrees) for plane 1

90. 0. 180. 5 = phi, thetan_min, thetan_max, dtheta (in degrees) for plane 2