Quasiparticle spectra and excitons of organic molecules deposited on substrates: G0W0-BSE approach applied to benzene on graphene and metallic substrates

We present an alternative methodology for calculating the quasi-particle energy, energy loss, and optical spectra of a molecule deposited on graphene or a metallic substrate. To test the accuracy of the method it is first applied to the isolated benzene (C6H6) molecule. The quasiparticle energy levels and especially the energies of the benzene excitons (triplet, singlet, optically active and inactive) are in very good agreement with available experimental results. It is shown that the vicinity of the various substrates (pristine/doped graphene or (jellium) metal surface) reduces the quasiparticle HOMO-LUMO gap by an amount that slightly depends on the substrate type. This is consistent with the simple image theory predictions. It is even shown that the substrate does not change the energy of the excitons in the isolated molecule. We prove (in terms of simple image theory) that energies of the excitons are indeed influenced by two mechanisms which cancel each other. We demonstrate that the benzene singlet optically active (E1u) exciton couples to real electronic excitations in the substrate. This causes it substantial decay, such as {\Gamma} = 174 meV for pristine graphene and {\Gamma} = 362 meV for metal surfaces as the substrate. However, we find that doping graphene does not influence the E1u exciton decay rate.Comment: 16 pages, 14 figure

Femtosecond laser driven molecular dynamics on surfaces: Photodesorption of molecular oxygen from Ag(110)

We simulate the femtosecond laser induced desorption dynamics of a diatomic molecule from a metal surface by including the effect of the electron and phonon excitations created by the laser pulse. Following previous models, the laser induced surface excitation is treated through the two temperature model, while the multidimensional dynamics of the molecule is described by a classical Langevin equation, in which the friction and random forces account for the action of the heated electrons. In this work, we propose the additional use of the generalized Langevin oscillator model to also include the effect of the energy exchange between the molecule and the heated surface lattice in the desorption dynamics. The model is applied to study the laser induced desorption of O$_2$ from the Ag(110) surface, making use of a six-dimensional potential energy surface calculated within density functional theory. Our results reveal the importance of the phonon mediated process and show that, depending on the value of the electronic density in the surroundings of the molecule adsorption site, its inclusion can significantly enhance or reduce the desorption probabilities.Comment: 11 pages, 8 figure

Femtosecond-laser induced dynamics of CO on Ru(0001): Deep insights from a hot-electron friction model including surface motion

Theoretical Chemistr

Influence of phenol and sugar interactions on antioxidant activity of pomegranate juice

Nowadays, people are focusing on antioxidant-rich food due to its beneficial effect on health. Thus, the goal of this study was to investigate the interactions between catechin, quercetin, and gallic acid in the presence of sugars (sucrose and trehalose) in complex food matrix such as pomegranate juice. Antioxidant activity (AOA) was measured by three different methods, DPPH and ABTS radical scavenging activity and ferric reducing antioxidant power (FRAP). In this paper, fundamental differences among used AOA measuring methods were confirmed, which can be traced back to interactions occurring between phenols and/or sugars. Even though addition of individual phenols increased AOA of mixtures, in the majority of binary and ternary mixtures antagonistic effects were observed. Positive effect of sugar addition was more pronounced in binary mixtures but the results were highly dependent on used AOA method

Imaging of Optically Active Defects with Nanometer Resolution.

Point defects significantly influence the optical and electrical properties of solid-state materials due to their interactions with charge carriers, which reduce the band-to-band optical transition energy. There has been a demand for developing direct optical imaging methods that would allow in situ characterization of individual defects with nanometer resolution. Here, we demonstrate the localization and quantitative counting of individual optically active defects in monolayer hexagonal boron nitride using single molecule localization microscopy. By exploiting the blinking behavior of defect emitters to temporally isolate multiple emitters within one diffraction limited region, we could resolve two defect emitters with a point-to-point distance down to ten nanometers. The results and conclusion presented in this work add unprecedented dimensions toward future applications of defects in quantum information processing and biological imaging

Scalable Authentication and Optimal Flooding in a Quantum Network

The global interest in quantum networks stems from the security guaranteed by the laws of physics. The deployment of quantum networks means facing the challenges of scaling up the physical hardware and, more importantly, of scaling up all other network layers and optimally utilizing network resources. Here, we consider two related protocols and their experimental demonstrations on an eight-user quantum network test bed, and discuss their usefulness with the aid of example use cases. First, we consider an authentication-transfer protocol to manage a fundamental limitation of quantum communication—the need for a preshared key between every pair of users linked together on the quantum network. By temporarily trusting some intermediary nodes for a short period of time (<35 min in our network), we can generate and distribute these initial authentication keys with a very high level of security. Second, when end users quantify their trust in intermediary nodes, our flooding protocol can be used to improve both end-to-end communication speeds and increase security against malicious nodes

Trendovi na tržištu mrkve u Republici Hrvatskoj

Iako je proizvodnja povrća jedna je od najdohodovnijih grana poljoprivredne proizvodnje u Hrvatskoj, povrće se uzgaja na svega 1% obradivih površina. Proizvodnja mrkve u sladu je s negativnim trendovima u proizvodnji povrća u Republici Hrvatskoj. Cilj rada bio je na temelju analiziranih podataka o proizvodnji povrća i mrkve prikazati trendove u proizvodnji i vanjskotrgovinskoj razmjeni mrkve u Republici Hrvatskoj te dati prijedloge za poboljšanje stanja. U radu su korišteni podaci Food and Agriculture Organization Corporate Statistical Database (FAOStat) o tržišnim pokazateljima u Europskoj uniji i Republici Hrvatskoj. Najveći proizvođači mrkve u EU u 2016. godini su Poljska (14,7 %), Velika Britanija (12,09 %), Njemačka (11,5 %), Nizozemska (10,7 %), Francuska (10,4 %) i Italija (9,5 %). Zadnjih desetak godina proizvodnja mrkve u RH stagnira i iznosi u prosjeku 10.588 t, a proizvodi se u prosjeku na 534 ha. Nepovoljni trend u proizvodnji odražava se i na negativnu vanjskotrgovinsku razmjenu mrkve, gdje izvoz čini samo 1,16 % izvoza mrkve. Povećanje proizvodnje mrkve i poboljšanje položaja proizvođača moguće je postići kroz ulaganje u razvoj, odnosno apliciranje zahtjeva za fondove Euopske unije namijenjene modernizaciji proizvodnje, kao i udruživanje malih proizvođača u cilju boljeg pozicioniranja na tržištu