Band structure of the spectra of Hamiltonians of regular polynucleotide duplexes

We calculate the band structure of the spectra of Hamiltonians of regular DNA duplexes and show that in single-stranded periodic polynucleotides whose period is determined by the number $m$ of nucleotides in an elementary cell, the spectrum consists of $m$ nonintersecting energy bands. In DNA duplexes, the number of energy bands is equal to $2m$, and the bands can intersect. Discrete energy levels can be present in forbidden bands in the case of (semi)bounded chains or duplexes.