THERMODYNAMICS OF A NONLINEAR MODEL FOR DNA DENATURATION

We study a model for the dynamical stretching of DNA which uses the stretching of the hydrogen bonds in a base-pair as its main variable. We present a statistical mechanical analysis of the denaturation and specific heat curves, obtained with the transfer integral method; discreteness effects are treated exactly by a numerical solution of the transfer integral operator. Second order self-consistent phonon theory agrees with the exact transfer integral results in the low and intermediate temperature range and explains the phonon softening observed in the molecular dynamics simulations. When the temperature approaches the denaturation temperature, the second order self-consistent phonon results deviate significantly from the exact ones, pointing to the fundamental role of nonlinear processes in DNA denaturation.