Optical Properties of Emeraldine Salt Polymers from Ab Initio Calculations: Comparison with Recent Experimental Data

We present absorption coefficient alpha(omega), transverse dielectric function epsilon(omega), optical conductivity sigma(omega), and reflectance R(omega) calculated for an emeraldine salt conducting polymer in its crystalline three-dimensional polaronic structure. We utilize Kohn-Sham DFT electronic wavefunctions and energies implemented in the expression of the macroscopic transverse dielectric function in the framework of the band theory without the electron-hole interaction. Contributions of intra-band transitions are taken into account by adding a Drude-like term to the dielectric function calculated ab initio. Comparison with optical properties, recently measured on high-quality emeraldine salts [Nature, (2006), 441, 65], and with optical absorption spectra, recorded on other emeraldine salts, is very satisfactory. The calculated spectra are discussed in terms of energy-band structure, density of states, inter- and intra-band transitions and transverse dielectric function.