General description of the methodology

M. Dlugosz and J. Trylska
Electrostatic similarity of proteins: Application of three dimensional spherical harmonic decomposition
THE JOURNAL OF CHEMICAL PHYSICS 129, 015103 (2008)

The Poisson-Boltzmann model

B. Honig, A. Nicholls
Classical Electrostatics in Biology and Chemistry
SCIENCE, 268:5214, 1144 (1995)

Spherical harmonic transforms, S2kit

D. Healy Jr., D. Rockmore, P. Kostelec and S. Moore
FFTs for the 2-Sphere – Improvements and Variations
THE JOURNAL OF FOURIER ANALYSIS AND APPLICATIONS 9:4, 341 (2003)

Hydrophobicity scale

G. D. Rose, A. Geselowitz, G. Lesser, R. Lee and M. Zehfus
Hydrophobicity of Amino Acid Residues in Globular Proteins
SCIENCE 229, 834 (1985)