First-Principles Description of Charge Transfer in Donor-Acceptor Compounds from Self-Consistent Many-Body Perturbation Theory

We investigate charge transfer in prototypical molecular donor-acceptor compounds using hybrid density functional theory (DFT) and the GW approximation at the perturbative level (G0W0) and at full self-consistency (sc-GW). For the systems considered here, no charge transfer should be expected at large intermolecular separation according to photoemission experiment and accurate quantum-chemistry calculations. The capability of hybrid exchange-correlation functionals of reproducing this feature depends critically on the fraction of exact exchange $\alpha$, as for small values of $\alpha$ spurious fractional charge transfer is observed between the donor and the acceptor. G0W0 based on hybrid DFT yields the correct alignment of the frontier orbitals for all values of $\alpha$. However, G0W0 has no capacity to alter the ground-state properties of the system, because of its perturbative nature. The electron density in donor-acceptor compounds thus remains incorrect for small $\alpha$ values. In sc-GW, where the Green's function is obtained from the iterative solution of the Dyson equation, the electron density is updated and reflects the correct description of the level alignment at the GW level, demonstrating the importance of self-consistent many-body approaches for the description of ground- and excited-state properties in donor-acceptor systems.Comment: 8 pages, 7 figure

Interface dipoles of organic molecules on Ag(111) in hybrid density-functional theory

We investigate the molecular acceptors 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA), 2,3,5,6-tetra uoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), and 4,5,9,10-pyrenetetraone (PYTON) on Ag(111) using densityfunctional theory. For two groups of the HSE(\alpha, \omega) family of exchange-correlation functionals (\omega = 0 and \omega = 0.2\AA) we study the isolated components as well as the combined systems as a function of the amount of exact-exchange (\alpha). We find that hybrid functionals favour electron transfer to the adsorbate. Comparing to experimental work-function data, we report for (\alpha) ca. 0.25 a notable but small improvement over (semi)local functionals for the interface dipole. Although Kohn-Sham eigenvalues are only approximate representations of ionization energies, incidentally, at this value also the density of states agrees well with the photoelectron spectra. However, increasing (\alpha) to values for which the energy of the lowest unoccupied molecular orbital matches the experimental electron affinity in the gas phase worsens both the interface dipole and the density of states. Our results imply that semi-local DFT calculations may often be adequate for conjugated organic molecules on metal surfaces and that the much more computationally demanding hybrid functionals yield only small improvements.Comment: submitted to New Journal of Physics (2013). More information can be found at http://th.fhi-berlin.mpg.de/site/index.php?n=Publications.Publication

Studies with Arylhydrazono-3-oxopropanals:A novel route to synthesis of substituted pyrazoles, oxoalkanonitrile and glyoxalonitrile containing sulfa drug moieties

Coupling of enaminones 1 with diazonium salts gave thehydrazonopropanals 3a-h. Compound 3 react with ω-bromoacetophenone or α-chloroacetanilide to yield 5 and 8. These compounds were cyclized smoothly into 6 and 9 respectively. Reactions of 3 with phenylhydrazine gave diphenylhydrazones 10 which cyclized into arylazopyrazoles 11 in refluxing pyridine. However reaction of 3c-f with hydrazine hydrate afforded pyrazoles 12.Reactions of 3 with phenylhydrazine hydrochloride afforded 11. Finally, reactions of 3c with hydroxylamine hydrochloride afforded the aldoxime 14 that on refluxing in pyridine gave 15 not 16

Investigations on the sensitivity of the relationships between sound absorption characteristics and microstructure related parameters for polyurethane foams

International audienceStraightforward semi-phenomenological models have been developed for highly porous polyurethane foams to predict the macroscopic nonacoustic parameters involved in the classical Johnson-Champoux-Allard model (i.e., porosity, airflow resistivity...) from microstructure properties (i.e, strut length, strut thickness and reticulation rate). These microstructure properties are measured using sophisticated optical methods (i.e., optical microscope, SEM) and a large variability can be observed due to great complexity of the 3D microstructure; variability which also depends on the precision of the measurement device. This work investigates how the variability associated with the model inputs affects the model outputs (i.e., non-acoustic parameters, surface impedance and sound absorption coefficient). The sensitivity analysis is based on the Fourier Amplitude Sensitivity Test (FAST). It helps quantify the correlation between the input parameters and identify the parameters contributing the most to output variability, thus requiring precise measurement. This study illustrates the preponderant impact of the reticulation rate (i.e, open pore content) on acoustic performances and guides the user on the required optical measurement device