Wire and extended ladder model predict THz oscillations in DNA monomers, dimers and trimers

We call $\mathit{\text{monomer}}$ a B-DNA base pair and study, analytically and numerically, electron or hole oscillations in $\mathit{\text{monomers}}$, $\mathit{\text{dimers}}$ and $\mathit{\text{trimers}}$. We employ two Tight Binding (TB) approaches: (I) at the base-pair level, using the on-site energies of the base pairs and the hopping parameters between successive base pairs i.e. \textit{a wire model}, and (II) at the single-base level, using the on-site energies of the bases and the hopping parameters between neighbouring bases, specifically between (a) two successive bases in the same strand, (b) complementary bases that define a base pair, and © diagonally located bases of successive base pairs, i.e. $\mathit{\text{an}}\mathit{\text{extended}}\mathit{\text{ladder}}\mathit{\text{model}}$ since it also includes the diagonal hoppings ©. For $\mathit{\text{monomers}}$, with TB II, we predict periodic carrier oscillations with frequency $f\approx$ 50-550 THz. For $\mathit{\text{dimers}}$, with TB I, we predict periodic carrier oscillations with $f \approx$ 0.25-100 THz. For $\mathit{\text{trimers}}\mathit{\text{made}}\mathit{\text{of}}\mathit{\text{identical}}\mathit{\text{monomers}}$, with TB I, we predict periodic carrier oscillations with $f\approx$ 0.5-33 THz. In other cases, either with TB I or TB II, the oscillations may be not strictly periodic, but Fourier analysis shows similar frequency content. For dimers and trimers, TB I and TB II are successfully compared giving complementary aspects of the oscillations.