On the energy gap determination of organic optoelectronic materials: the case of porphyrin derivatives

A correct determination of the ionization potential (IP) and electron affinity (EA) as wells as the energy gap is essential to properly characterize a series of key phenomena related to...

The GW Miracle in Many-Body Perturbation Theory for the Ionization Potential of Molecules

We use the GW100 benchmark set to systematically judge the quality of several perturbation theories against high-level quantum chemistry methods. First of all, we revisit the reference CCSD(T) ionization potentials for this popular benchmark set and establish a revised set of CCSD(T) results. Then, for all of these 100 molecules, we calculate the HOMO energy within second and third-order perturbation theory (PT2 and PT3), and, GW as post-Hartree-Fock methods. We found GW to be the most accurate of these three approximations for the ionization potential, by far. Going beyond GW by adding more diagrams is a tedious and dangerous activity: We tried to complement GW with second-order exchange (SOX), with second-order screened exchange (SOSEX), with interacting electron-hole pairs (WTDHF), and with a GW density-matrix (γGW). Only the γGW result has a positive impact. Finally using an improved hybrid functional for the non-interacting Green’s function, considering it as a cheap way to approximate self-consistency, the accuracy of the simplest GW approximation improves even more. We conclude that GW is a miracle: Its subtle balance makes GW both accurate and fast.

Lead evaporation by VUV radiation of various spectral ranges

The results of an experimental study of the plasma formed by the evaporation of the lead target in the field of powerful broadband VUV radiation are presented. A pulse light-erosion magnetoplasma compressor (MPC’s) discharge is used as a model source of VUV radiation. “Gas filtration” of radiation is used to control the spectral composition – the discharge takes place in pure inert gases: in argon at 200 torr and neon at 400 torr. This allows us to manage the spectral distribution of radiation energy and to limit the energy of quants which irradiate the lead target with the first ionization potential of buffer gas. Shadow photography, toeplergrathy, double exposure laser holographic interferometry are used for diagnostics. Experimentally established different distribution of parameters in the lead plasma depending on the spectral composition of the impact radiation (the composition of buffer gas). It is shown that when the energy of quants increases (above the lead second ionization potential), a more even heating of the plasma layer is realized.

Observing meteors by creating artificial luminous clouds in the Earth’s atmosphere

В статье дается предварительная теоретическая оценка возможности применения нового способа наблюдения метеоров в атмосфере Земли с помощью искусственных светящихся облаков. При попадании метеоров в такие облака, образованные веществом с потенциалом ионизации в несколько раз меньшем потенциала ионизации атмосферных газов, происходит быстрая ионизация реагента облака за счет термического и ударного воздействия метеорного тела, приводящая к увеличению светимости метеорных следов. Предполагается, что такой эффект будет способствовать увеличению яркости слабых метеоров, находящихся на пороге обнаружения современных телевизионных камер. Это позволит проводить исследования метеоров и метеорных потоков, доступных ранее только радиолокационными методами наблюдения. The article provides a preliminary theoretical assessment of the possibility of using a new method of observing meteors in the Earth’s atmosphere using artificial luminous clouds. When meteors hit such clouds formed by a substance with an ionization potential several times lower than the ionization potential of atmospheric gases, the cloud reagent is rapidly ionized due to the thermal and impact effects of the meteor body, which leads to an increase in the luminosity of meteor tracks. It is assumed that this effect will increase the brightness of weak meteors, which are on the threshold of detection by modern TV cameras. This will make it possible to conduct studies of meteors and meteor showers that were previously available only by radar observation methods.

Investigation Ability of Two-Dimensional Nano Materials for Detection Toxic Gases

In this study, pure graphene nano-ribbon were used to detect toxic gases under study, which are carbon monoxide, hydro cyanide and methane. The study focused on describing graphene nano-ribbons as sensors for these gases and their use in environmental applications. Quantitative computing methods have been used to calculate the properties of the ground state by density function theory (DFT) and the properties of the stationary state, it was computed by using the time-dependent Schrödinger equation. Ground-state calculations include geometric optimization, total energy, ionization potential, electron affinity, molecular orbit energies, energy gap, adsorption energy and infrared spectrum. Whereas, the time-dependent Schrödinger equation calculations included the UV-Visible spectrum calculations, in order to characterize them as detectors of toxic gases. It was found by studying the adsorption of pure graphene nano-ribbons is sensitive to carbon monoxide, clearly and higher than hydro cyanide and methane. Also, as a result of the chemical reaction, there is a clear effect on the values of the energy gap, the ionization potential, and other associated properties. The effect of the chemical reaction continues at an adsorption distance of 2 angstroms from the surface. As for the infrared radiation calculations, it showed that the appearance of free radicals of adsorbed gases on the surface of the nano-ribbons is a clear evidence of the occurrence of chemical reaction with high energy. Through the results, the calculations of the UV-visible spectrum showed a clear shift in the computed spectrum at the ranges of high-energy interaction (34.0385-22.3212) and (15.7433-3.3246) electron volts for both nano-ribbons.