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Perturbation Theory in the Analysis of Quantum Vortices Formed by Impact of Ultrashort Electromagnetic Pulse on Atom
摘要： Nonstationary perturbation theory is used to study generation of quantum vortices resulting from ionization of hydrogen-like atom by an ultrashort pulse of classical electromagnetic field. It is shown that the vortices are determined by quantum interference effects.
关键词： quantum vortices,hydrogen-like atom,quantum interference effects,classical electromagnetic field,nonstationary perturbation theory,ultrashort pulse
更新于2025-09-09 09:28:46
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Vibrational properties of germanane and fluorinated germanene in the chair, boat, and zigzag-line configurations
摘要： The electronic and vibrational properties of germanane and fluorinated germanene are studied within Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) frameworks. Different structural configurations of germanane and fluorinated germanene are investigated. The energy difference between the different configurations are consistently smaller than the energy of thermal fluctuations for all the analyzed DFT functionals LDA, GGA, and hybrid functionals, which implies that, in principle, it is possible to find these different configurations in different regions of the sample as minority phases or local defects. We calculate the Raman and infrared spectra for these configurations by using ab initio calculations and compare it with available experimental spectra for germanane. Our results show the presence of minority phases compatible with the configurations analyzed in this work. As these low energy configurations are metaestable, the present work shows that the synthesis of these energy competing phases is feasible by selectively changing the synthesis conditions, which is an opportunity to expand in this way the availability of new two-dimensional compounds.
关键词： Density Functional Perturbation Theory,germanane,fluorinated germanene
更新于2025-09-09 09:28:46
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First-principles study of structural phase transformation and dynamical stability of cubic AlN semiconductors
摘要： Phase transformation and stability of cubic aluminium nitride (AlN) phases such as zinc-blende and rock-salt have been investigated using first-principles calculations based on density functional perturbation theory (DFPT) within quasi-harmonic approximation (QHA). The phonon dispersion relations of both the cubic phases have been calculated at various high-symmetry points of the Brillouin Zone. The pressure and volume dependence of phonon frequencies have been investigated. The application of pressure results in opposite trend of transverse acoustic (TA) phonon frequencies for rock-salt and zinc-blende AlN phases. The TA frequencies found to increase for the former one and decrease for the latter one with the increase in pressure. The dynamical instability results in a volume expansion of rock-salt AlN close to the equilibrium volume of zinc-blende AlN. Phase transformation of these cubic phases is further investigated by computing an equilibrium pressure-temperature phase diagram within QHA. The cubic rock-salt AlN is found to form at high pressures and temperatures than zinc-blende AlN. The temperature dependence of lattice constant and the corresponding volume thermal expansion coefficient of both the cubic phases have been investigated.
关键词： Aluminium nitride,First-principles calculations,Density functional perturbation theory,Quasi-harmonic approximation,Phase transformation,Dynamical stability
更新于2025-09-09 09:28:46