Effective-phonon theory for DNA melting

The melting of the DNA double helix is treated within an effective-phonon theory for a simplified model of a double strand of particles (nucleotides) interacting through harmonic stacking forces and anharmonic hydrogen bonds represented by potentials V(u)=1/2${\mathit{Bu}}^2$-Cγ${\mathit{u}}^3$. Analytical expressions are given for the melting temperature and the critical bond stretch, as well as for the temperature scaling of the entropy and heat capacity below the critical point. The model also accommodates a broad low-frequency band at 85 ${\mathrm{cm}}^{\mathrm{-}1}$, which softens with increasing temperature.