PPP Hamiltonian for polar polycyclic aromatic hydrocarbons E. San-Fabián, A. Guijarro, J. A. Vergés, G. Chiappe and E. Louis Eur. Phys. J. B, 81 2 (2011) 253-262 Published online: 25 May 2011 DOI: 10.1140/epjb/e2011-20094-1