DOI: 10.5281/zenodo.16581692
title: "Mie" Coefficients for Fractal Aggregates for the Virga Exoplanet Cloud Model (Virga V2)

description: These files are used to compute parameterized cloud models with the Virga Exoplanet Cloud Model under the V2 version, which includes non-spherical particles as fractal aggregate particles following Modified Mean Field Theory (MMF; Tazaki and Tanaka 2018; Tazaki 2021) as implemented into the open source code OpTool.

The method used to generate these grids is fully desribed in Moran & Lodge et al 2025.

All refractive indices used to generate Mie coefficients are included here for completeness, but are identical to those used in the spherical version of virga, V1.0 and V0. 

1. REFRACTIVE INDICES: (.refrind): contain the refractive indices of each condensate species. If you are running cloud models utilizing this data, please cite the corresponding source for each species listed below. All files are 4 columns structured as : 



index, wavelength (micron), real part, imaginary part. 


Virga reads in these files in this routine but you can simply use this python code:

filename = "H2O.refrind"
idummy, wave, nn, kk = np.loadtxt(open(filename,'rt').readlines(), unpack=True, usecols=[0,1,2,3])#[:-1]


 

2. "MIE" PARAMETERS from MMF Theory: (.mieff): Here we include the "Mie" coefficients calculated using MMF for our range of fractal shapes (characterized by the fractal number, Df, with values of 1.2, 1.6, 2.0, 2.4, and 2.8, where 1.2 is a highly linear aggregate and 2.8 is nearly spherical) for particles with fixed monomer numbers of 1000. Particle sizes, in terms of an equivalent compact sphere, range from 0.001 to 100 microns with 40 log-spaced radii gridpoints. Mie coefficients are calculated from 0.268 to 29.7 microns. Spherical files are included as well, and are denoted by the lack of "Df" in the file name.

There are specific tutorials and functions in virga V2.0 that will guide you through computing these on your own. However, we provide them here for completeness. Note that, as with (spherical) virga v1.0, each set of Mie parameters are averaged 6 points within the wavelength bin. You can use this function here to parse the data. Or, you can simply read the mieff files with this code: 

import pandas as pd
gas = "H2O"
df = pd.read_csv(gas+".mieff",names=['wave','qscat','qext','cos_qscat'], delim_whitespace=True)


 

CITATIONS TO REFERENCE FOR EACH SPECIES:

KCl 

-note! These differ from the version used in Moran and Lodge et al. (2025), which used those of Palik (1985).

Querry, Marvin R. Optical constants of minerals and other materials from the millimeter to the ultraviolet. Chemical Research, Development & Engineering Center, US Army Armament Munitions Chemical Command, 1987.

ZnS

Querry, Marvin R. Optical constants of minerals and other materials from the millimeter to the ultraviolet. Chemical Research, Development & Engineering Center, US Army Armament Munitions Chemical Command, 1987.

MnS 

Huffman, Donald R., and Robert L. Wild. "Optical Properties of α− M n S." Physical Review 156.3 (1967): 989.

Cr

Stashchuk, V. S., M. Ts Dobrovolskaya, and S. N. Tkachenko. "Optical properties and electronic characteristics of chromium." Optics and Spectroscopy 56 (1984): 594-596.

Na2S

Montaner, Antoine, et al. "Optical constants of sodium sulphide." Physica Status Solidi. A, Applied Research 52.2 (1979): 597-601.

Khachai, H., et al. "FP-APW+ lo calculations of the electronic and optical properties of alkali metal sulfides under pressure." Journal of Physics: Condensed Matter 21.9 (2009): 095404.

MgSiO3 & Mg2SiO4

Scott, A., and W. W. Duley. "Ultraviolet and infrared refractive indices of amorphous silicates." The Astrophysical Journal Supplement Series 105 (1996): 401.

Fe

Leksina, I., N. Penkina, and Fizik Metall Metalloved. "Optical characteristics of iron in the visual and near infrared spectral regions." Fizik. Metall. Metalloved 23 (1967): 344-345.

Al2O3

Koike, Chiyoe, et al. "Extinction spectra of corundum in the wavelengths from UV to FIR." Icarus 114.1 (1995): 203-214.

NH3

Martonchik, John V., Glenn S. Orton, and John F. Appleby. "Optical properties of NH 3 ice from the far infrared to the near ultraviolet." Applied optics 23.4 (1984): 541-547.

ALL ELSE

Th. Henning, V.B. Il'in, N.A. Krivova, B. Michel, and N.V. Voshchinnikov (1999) WWW database of optical constants for astronomy. Astron. Astrophys. Suppl. 136, 405.

C. Jaeger, V.B. Il'in, Th. Henning, H. Mutschke, D. Fabian, D.A. Semenov, and N.V. Voshchinnikov (2002) A database of optical constants of cosmic dust analogs. J. Quant. Spectrosc. Rad. Transf.

https://www.astro.uni-jena.de/Laboratory/Database/jpdoc/f-dbase.html