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13C NMR chemical shifts of pristine fullerene have been studied computationally using gauge–independent atomic orbital (GAIO) and density functional theory (DFT). The molecular structure of C60 were optimized by DFT/B3LYP method with 6-31G basis set using Gaussian 09 program. The shielding constants for 13C atom have been calculated by GIAO/B3LYP/6-31G(d,p) approach and analyzed both in gas and solvent phases. The solvent effect is mimicked by PCM polarizable continuum model. A single sharp line in the nuclear magnetic resonance spectrum is observed. The NMR spectra of the investigated compound are in good agreement with the structures optimized by DFT calculations. With the shielding magnetic tensor (GIAO), the magnetic shielding density and magnetically induced current density with the mapped surface for the nucleus of the molecule were simulated and analyzed. The results indicate that the complete information may be obtained from 13C NMR of pristine fullerene. The high symmetrical nature of the sample paves way for designing the bioactive materials which will be useful in the field of carbon nano medicine and targeted drug delivery applications.

The shallow-donor ground-state binding energy of wurtzite strained (In,Ga)N asymmetric coupled quantum wells (ACQW) is calculated. Within the effective-mass and the one-band parabolic approximations, the structure size, the composition of well and the barrier, the position of the impurity and the built-in electric field effects are investigated using a variational approach under finite confinement potential. The competition effect between the quantum confinement potential and the BEF is also shown. Our results reveal that the binding energy is the largest at a point corresponding to the maxima of the electron wave-function and a larger value is obtained compared to uncoupled QWs. Moreover, the principle effect of the BEF is to reduce the binding energy. It is established that the binding energy can be easily modulated by modifying the structure size, its constitution and the impurity׳s position.

The effect of longitudinal optical phonon field on the exciton in a Cd 1 − x o u t Mn x o u t Te / Cd 1 − x i n Mn x i n Te / Cd 1 − x o u t Mn x o u t Te strained quantum well is investigated using the Aldrich–Bajaj effective potential. Spin polaronic shifts are estimated using mean field theory for different Mn concentration and the well sizes. A theoretical study of diluted magnetic semiconductors treating local sp-d exchange interaction J between the itinerant carriers and the Mn electrons is treated within a realistic band structure. The total optical absorption and the refractive index changes as a function of normalized photon energy in the presence of polaron and the Mn ion content are analyzed. Our results show that the occurred red shifts of the absorption resonant peak due to the polaron in CdMnTe give the information about the variation of two energy levels in the quantum well. The optical absorption coefficients and the refractive index changes strongly depend on the incident optical intensity, the polaronic effect and the Mn content.

Effect of laser field intensity on exciton binding energies is investigated in a GaAs/ GaAlAs double quantum well system. Calculations have been carried out with the variational technique within the single band effective mass approximations using a two parametric trial wave function. The interband emission energy as a function of well width is calculated in the influence of laser field. The laser field induced photoionization cross-section for the exciton placed at the centre of the quantum well is computed as a function of normalized photon energy. The dependence of the photoionization cross-section on photon energy is carried out for the excitons. The resulting spectra are brought out for light polarized along and perpendicular to the growth direction. The intense laser field dependence of interband absorption coefficient is investigated. The results show that the exciton binding energy, interband emission energy, the photoionization cross-section and the interband absorption coefficient depend strongly on the well width and the laser field intensity. Our results are compared with the other existing literature available.

Exciton states confined in a GaN/Ga1−xAlxN Quantum dot are investigated within the framework of single band effective mass approximation. Charged donor bound exciton, D + X energy is computed as a function of dot radius for different Al concentration and the height of cylindrical dot. The interband optical transition of GaN/Ga1−xAlxN dot is calculated with the various structural parameters. The valence band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. Binding energy of the ground state of exciton is calculated, with the inclusion of 2D Hartree dielectric screening function. Our results show that quantum size has a considerable influence on exciton states and interband optical transitions of the narrow dots. The ground state exciton binding energy and the interband emission energy are increased when the cylindrical quantum dot height or radius is decreased and the effect of exciton has influence on the interband emission energy. The donor bound exciton binding energy increases monotonically as Al concentration increases. Our results are compared with the existing available literature.

We investigate the effects of magnetic field strength over the ground state binding energy of a hydrogenic acceptor impurity confined in a Cd 1 − x i n Mn x i n Te / Cd 1 − x o u t Mn x o u t Te quantum well. We apply the variational method using 1s-hydrogenic wavefunction, in the framework of the single band effective mass approximation. The effect of valence band degeneracy is considered through the energy dependent effective mass. The magnetic field dependence of the barrier height is discussed. The band gap tuning in an external magnetic field for different compositions of Mn ions is achieved using an empirical formula. Spin polaronic shifts are estimated using mean field theory for different magnetic field strengths and the well sizes. We present a theoretical study of diluted magnetic semiconductors treating the local p–d exchange interaction J between the itinerant carriers and the Mn electrons within a realistic band structure. These results are compared with the other existing available literature.

The donor bound spin polaron in a Cd1−xMnxTe quantum dot is investigated theoretically. Spin polaronic shifts are estimated using a mean field theory. Magnetization is calculated for various concentrations of Mn2+ ions with the dot sizes. The lowest binding energies in a diluted magnetic semiconductor of a Cd1−xMnxTe quantum dot are also estimated. Using the effective mass approximation, calculations are presented with and without spatial dependent effective masses. It is found that (i) the lowest binding energy decreases with the dot radius (ii) position dependent mass gives larger binding energy for smaller dots (iii) the ionization energy becomes more when spin interaction energy is included (iv) variation of increase in ionization energy is sharper for smaller dots with increase in concentration and (v) the magnetization of Mn subsystem increases when concentration of Mn2+ ions increases and it has appreciable changes for smaller dots.

The binding energy of shallow hydrogenic impurities in parabolic quantum dots is calculated using a variational approach within the effective mass approximation. The binding energies are worked out for GaAs/Ga1−xAlxAs structures as a function of dot size when the static pressure and the magnetic field are applied simultaneously. The results show that the impurity binding energy (i) increases with the reduction in dot sizes for a given pressure and magnetic field; (ii) decreases for a given dot in the presence of pressure; (iii) increases for a given dot by the influence of magnetic field and (iv) increases for a given dot in the presence of pressure and magnetic field applied simultaneously. The result shows that the ionization energy is purely pressure dependent for dots of size less than an effective Bohr radius. The results are compared with available data in the literature.

Ionization energies of a shallow donor in a quantum well of GaAs/Ga 1− x Al x As superlattice system in the influence of pressure using a variational procedure within the effective mass approximation are obtained. The vanishing of ionization energy triggering a Mott transition is observed within the one-electron approximation. The effects of Anderson localization, exchange and correlation in the Hubbard model are included in this model. It is found that the ionization energy (i) increases as well width increases for a given pressure (ii) increases when well width increases and (iii) the critical concentration at which the metal–insulator transition occurs is increased when pressure is applied. All the calculations have been carried out with finite and infinite barriers and the results are compared with available data in the literature.