The theory of charge pumping through a quantum wire is considered in the tight binding approximation. By introducing the Ricatti operator in the Hilbert space of the side-band states (Floquet states) we drive the Ricatti equation for a quantum wire driven by a time-periodic potential. Then a recursive method is developed for numerical calculation of the Floquet scattering matrix by expressing the right and left transmission and reflection operators in terms of the Ricatti operator. We then apply the method to the problem of charge pumping in a quantum wire attached to leads where the time-periodic potential (harmonic, pulsed and triangular) is applied to two sites of the wire. Finally, we show that the pumped current as a function of the wire–lead coupling shows a sign reversal.

Using the Hartree-Fock and single configuration interaction model in conjunction with the local field method, the dielectric tensor, refractive index, circular dichroism, birefringence coefficient and the effects of spatial dispersion on the spectrum of the transverse normal polariton waves of the simple cubic phase of the C 60 crystal are calculated. Our results on magneto-optical circular dichroism in the energy range 3-4 eV almost reproduces the reported experimental results. Also, our results on the effect of spatial dispersion, compared with the non-dispersive case, indicate that the first branch of the transverse normal polariton in the C 60 crystal is due to the coupling of the second excitonic state of the C 60 molecule with the electromagnetic field and the first excitonic state has very weak coupling.

Using the Hartree–Fock Su–Sheriffer–Heeger model and the sum-over-state method the linear and nonlinear polarizabilities, the dc Stark effect and the degenerate two-photon absorption (TPA) cross sections of the small-size trigonal zigzag graphene nanoflakes (TZGNs) have been investigated. The obtained dispersion spectra of the second- and third-order polarizabilities and the degenerate TPA cross sections of size-2 and size-3 TZGNs, which, respectively, have 22 carbon atoms with two edge states and 33 carbon atoms with three edge states, show peak values of the order of 10−28 esu, 10−32 esu and 103 GM, respectively. Furthermore, even-size TZGNs show electrostatic induced transparency due to their sizable dc Stark effect, which makes them suitable for linear and nonlinear optoelectronic devices.

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