Predicting Solid-State Heats of Formation of Newly Synthesized Polynitrogen Materials by Using Quantum Mechanical Calculations

We present density functional theory level predictions and analysis of the basic properties of newly synthesized high-nitrogen compounds together with 3,6-bis(2H-tetrazol-5-yl)-1,2,4,5-tetrazine (BTT) and 3,3′-azobis(6-amino-1,2,4,5-tetrazine) (DAAT), for which experimental data are available. The newly synthesized high-nitrogen compounds are based on tricycle fused 1,2,4-triazine and 1,2,4,5-tetrazine heterocycles. In this work, the molecules BTT and DAAT have been studied in order to validate the theoretical approach and to facilitate further progress developments for the molecules of interest. Molecular structural properties are clarified, and IR spectra predictions are provided to help detection of those compounds in the experiment. The energy content of the molecules in the gas phase is evaluated by calculating standard enthalpies of formation, by using a special selection of isodesmic reaction paths. We also include estimates of the condensed-phase heats of formation and heats of sublimation in the framework of the Politzer approach. The obtained properties are consistent with those new high-nitrogen compounds being a promising set of advanced energetic materials

Modeling A.C. Electronic Transport through a Two-Dimensional Quantum Point Contact

We present the results on the a.c. transport of electrons moving through a two-dimensional (2D) semiconductor quantum point contact (QPC). We concentrate our attention on the characteristic properties of the high frequency admittance ({omega}{approximately}0 - 50 GHz), and on the oscillations of the admittance in the vicinity of the separatrix (when a channel opens or closes), in presence of the relaxation effects. The experimental verification of such oscillations in the admittance would be a strong confirmation of the semi-classical approach to the a.c. transport in a QPC, in the separatrix region

A.c. transport and collective excitation in a quantum point contact

The authors calculate the a.c.-admittance of a two dimensional quantum point contact (QPC) using a Boltzmann-like kinetic equation derived for the partial Wigner distribution function. An integral equation for a potential inside a QPC is solved numerically. The dependence of the admittance on the frequency of the a.c. field is found in a wide frequency range {omega} {approx} 0--50 GHz. The contribution to the imaginary part of the admittance due to the quantum capacitance and inductance is numerically calculated. It is shown that the crossover from localized parameters--quantum capacitance and inductance--to distributed behavior takes place at {omega} {approximately} 10 GHz. A transition from 2D plasmons to quasi-1D plasmons is analyzed as a function of two dimensionless parameters: k{sub x}d{sub 0} (where k{sub x} is the longitudinal wave vector, and d{sub 0} is the width of the QPC), and the number of open electron channels, N

High Energy Optical Transitions in Ga(PN): Contribution from Perturbed Valence Band

The GaP1-xNx conduction band is investigated experimentally (by excitation photoluminescence) and theoretically (by pseudopotential supercells) for N concentrations up to x=3.5% and photon energies ranging from the optical absorption edge to 3.2 eV. With increasing x: (i) a direct-like absorption edge develops smoothly and red-shifts rapidly overtaking energy-pinned cluster states; (ii) a broad absorption plateau appears between the X1c and the Γ1c critical points of GaP; (iii) the Γ1c absorption edge broadens and gradually disappears. Empirical pseudopotential calculations for GaP1-xN x random alloy supercells account well for all the PLE results by considering N induced changes in the valence band overlooked so far. © 2005 American Institute of Physics