Optical conductivity of wet DNA

Motivated by recent experiments, we study the optical conductivity of DNA in its natural environment containing water molecules and counterions. Our density functional theory calculations (using Siesta) for four base pair B-DNA with order 250 surrounding water molecules suggest a thermally activated doping of the DNA by water states which generically leads to an electronic contribution to low-frequency absorption. The main contributions to the doping result from water near DNA ends, breaks, or nicks and are thus potentially associated with temporal or structural defects in the DNA.