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A. Shafiekhani

Publications and source records attributed to A. Shafiekhani.

11 recordsLinked to original sources
arXiv2012

The Ground State of Graphene and Graphene Disordered by Vacancies

Graphene clusters consisting of 24 to 150 carbon atoms and hydrogen termination at the zigzag boundary edges have been studied, as well as clusters disordered by vacancy(s). Density Function Theory and Gaussian03 software were used to calculate graphene relative stability, desorption energy, band gap, density of states, surface shape, dipole momentum and electrical polarization of all clusters by applying the hybrid exchange-correlation functional Beke-Lee-Yang-Parr. Furthermore, infrared frequencies were calculated for two of them. Different basis sets, 6-31g**, 6-31g* and 6-31g, depending on the sizes of clusters are considered to compromise the effect of this selection on the calculated results. We found that relative stability and the gap decreases according to the size increase of the graphene cluster. Mulliken charge variation increase with the size. For about 500 carbon atoms, a zero HOMO-LUMO gap amount is predicted. Vacancy generally reduces the stability and having vacancy affects the stability differently according to the location of vacancies. Surface geometry of each cluster depends on the number of vacancies and their locations. The energy gap changes as with the location of vacancies in each cluster. The dipole momentum is dependent on the location of vacancies with respect to one another. The carbon-carbon length changes according to each covalence band distance from the boundary and vacancies. Two basis sets, 6-31g* and 6-31g**, predict equal amount for energy, gap and surface structure, but charge distribution results are completely different.

cond-mat.mes-hall↗
arXiv2012

Graphene/Li-Ion battery

Density function theory calculations were carried out to clarify storage states of Lithium (Li) ions in graphene clusters. The adsorption energy, spin polarization, charge distribution, electronic gap, surface curvature and dipole momentum were calculated for each cluster. Li-ion adsorbed graphene, doped by one Li atom is spin polarized, so there would be different gaps for different spin polarization in electrons. Calculation results demonstrated that a smaller cluster between each two larger clusters is preferable, because it could improve graphene Li-ion batteries; consequently, the most proper graphene anode structure has been proposed.

cond-mat.mtrl-sci↗
arXiv2012

Spin polarized diamond neutral vacancy

The atomic orbital basis and atomic pseudopotential for electron-ion interaction in framework of density function theory used to calculate C70H84 spin polarized diamond cluster with neutral vacancy. The band gap has been found to be 1.70 eV. The chosen cluster comprises electronic properties depending on thetype of its spin. It could be used as a data transporter. The calculated band gap, density of state and spin properties illustrate how beneficial it could be in spintronic devices.

cond-mat.mtrl-sci↗
arXiv2001

The Composition Lines of the Visible Band of Synthetic Diamond

The visible band (band A) of Photoluminescence spectra of high-purity synthesized diamond is analyzed by deconvolution technique. A set of eight lines with distinct peak energy are found. The peak energy and the width of these lines were either constant or varies very slightly with temperature. The amplitude of the lines are significantly temperature. The closeness of the temperature that the amplitudes of these lines reach their minimum and the temperature which the Free-exiton emission is maximum at, is an indication of the competition between these too effects.

cond-mat.mtrl-sci↗
arXiv1998

Jahn-Teller Effect in Diamond-like Carbon Film

The Jahn-Teller effect used semi-theoretically to analyse UV-visible spectra of the diamond like-carbon films on Si substrates. By deconvolution of UV-visible absorption spectra of the typical films, different absorption lines found. For each sample, six lines which were related to $\V^\circ$ by Jahn-Teller effect are distinguished. Our theoretical approach based on distortion of the $\V^\circ$ as the consequence of the stress in the films, is in agreement with experimental results. The shift of the Jahn-Teller lines toward the zero phonon line of $\V^\circ$ were found in accordance to stress decrease in the films. The difference between room temperature and low temperature spectra is discussed. We found that the splitting of the excited state of $\V^\circ$ in the films under stress is twice as large as that of the ground state.

cond-mat.mtrl-sci↗
arXiv1998

N=2 Super-Conformal Filed Theory on the Basis of osp(2|2)

Using a unified and systematic scheme, the free field realization of irreducible representations of osp(2|2) is constructed. By using these realization, the correlation functions of N=2 super-conformal model based on osp(2|2) symmetry and free field representation of ${\hat{osp(2|2)}}$ generators are calculated. Free field representation of currents are used to determine the stress-energy tensor and the central charge of the model.

hep-th↗
arXiv1998

Diamond-Like Carbon film from Liquid Gas on Metallic Substrates

Liquid gas was used to produce DLC films on Cu, Al and steel substrates by DC plasma technique. The absorption in IR reflectance indicates, grown films are DLC. By deconvolution of room temperature UV-visible spectra of the films grown at 50 mtorr and 200${}^\circ$C, in addition to the spectra lines reported for CL, PL, PLC and ESR, some new spectra lines were obtained. We also, have seen exciton absorption line at room temperature.

cond-mat.mtrl-sci↗
arXiv1997

Exactly and Quasi-Exactly Solvable Models on the Basis of $osp(2|1)$

The exactly and quasi-exactly solvable problems for spin one-half in one dimension on the basis of a hidden dynamical symmetry algebra of Hamiltonian are discussed. We take the supergroup, $OSP(2|1)$, as such a symmetry. A number of exactly solvable examples are considered and their spectrum are evaluated explicitly. Also, a class of quasi-exactly solvable problems on the basis of such a symmetry has been obtained.

hep-th↗
arXiv1997

Logarithmic Operators in Conformal Field Theory and The $\W_\infty$-algebra

It is shown explicitly that the correlation functions of Conformal Field Theories (CFT) with the logarithmic operators are invariant under the differential realization of Borel subalgebra of $\W_\infty$-algebra. This algebra is constructed by tensor-operator algebra of differential representation of ordinary $sl(2,C)$. This method allows us to write differential equations which can be used to find general expression for three and four-point correlation functions possessing logarithmic operators. The operator product expansion (OPE) coefficients of general logarithmic CFT are given up to third level.

hep-th↗
arXiv1996

Free Field Representation of $osp(2|1)$ and $U_q(osp(2|1))$ and N=1 (q-)Superstring Correlation Functions

The free field realization of irreducible representations of $\os$ is constructed, by a unified and systematic scheme. The $q$-analog of this unified scheme is used to construct $q$-free field realization of irreducible representations of $\uos$. By using these realization, the two point function of $N=1$ superconformal (q-superconformal) model based on $\os$ ($\uos$) symmetry have been calculated.

hep-th↗