On the theory of charge transfer energies at donor-acceptor interfaces in solar cells

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Charge transfer states at the donor–acceptor interface in organic solar cells determine the device performance. Therefore a basic description, understanding and estimation of the energetics of the charge transfer states at donor-acceptor interfaces are crucial for the improvement of the efficiency especially of organic solar cells. In the presentation, we report about the results of theoretical studies on donor–acceptor combinations used in molecular solar cells. As an example, we discuss especially zinc phthalocyanine – C60 blends. Several computational schemes based on constrained density functional theory (c-DFT), Hartree-Fock based configuration interaction of singles (CIS) and time-dependent density functional theory (TD-DFT) using the hybrid functional B3LYP were used to assess the energy of the lowest charge transfer (CT) state in such systems. The results of the calculations are discussed in comparison with available spectroscopic data, and in comparison with solid state calculations. For example, the results from c-DFT and CIS calculations reproduce the correct Coulomb asymptotics between cationic donor and anionic acceptor configurations, whereas TD-DFT gives qualitatively wrong excitation energies.cf201

Large adaptive optics survey for substellar objects around Young, Nearby, Low-mass Stars with Robo-AO

We present results from the Large Adaptive optics Survey for Substellar Objects, where the goal is to directly image new substellar companions (<70 MJup) at wide orbital separations (≳50 au) around young (≲300 Myr), nearby (<100 pc), low-mass (≈0.1–0.8 M☉) stars. We report on 427 young stars imaged in the visible (i′) and near-infrared (J or H) simultaneously with Robo-AO on the Kitt Peak 2.1 m telescope and later the Maunakea University of Hawaii 2.2 m telescope. To undertake the observations, we commissioned a new infrared camera for Robo-AO that uses a low-noise high-speed SAPHIRA avalanche photodiode detector. We detected 121 companion candidates around 111 stars, of which 62 companions are physically associated based on Gaia DR2 parallaxes and proper motions, another 45 require follow-up observations to confirm physical association, and 14 are background objects. The companion separations range from 2 to 1101 au and reach contrast ratios of 7.7 mag in the near-infrared compared to the primary. The majority of confirmed and pending candidates are stellar companions, with ∼5 being potentially substellar and requiring follow-up observations for confirmation. We also detected a 43 ± 9 MJup and an 81 ± 5 MJup companion that were previously reported. We found 34 of our targets have acceleration measurements detected using Hipparcos–Gaia proper motions. Of those, 58-+1412% of the 12 stars with imaged companion candidates have significant accelerations (c2 > 11.8), while only 23-+611% of the remaining 22 stars with no detected companion have significant accelerations. The significance of the acceleration decreases with increasing companion separation. These young accelerating low-mass stars with companions will eventually yield dynamical masses with future orbit monitoring

High contrast imaging upgrades for the Keck adaptive optics imager

The Keck II adaptive optics (AO) system is being upgraded with a near-infrared Pyramid Wavefront Sensor (PWS) as part of the Keck Planet Imager and Characterizer (KPIC) upgrade. The overview of the KPIC project and the PWS development are presented elsewhere in this conference. This paper focuses on improvements made to the NIRC2 science instrument, referred to as the NIRC2 upgrade, aimed at enhancing its high contrast imaging capabilities. The NIRC2 upgrade incorporates new coronagraphic elements that reach their maximum performance when operated in combination with the new near-infrared PWS and polarimetric elements that would add polarimetric capability when fully implemented. The key elements to the NIRC2 upgrade are the installation of two next-generation Vector Vortex Coronographic (VVC) masks, one optimized for the L and M band, and the other one optimized for the K band. Also key to the upgrade is the incorporation of a new Lyot stop optimized to minimize diffraction and residual nutation of the Keck-II telescope pupil. These new elements provide improved coronographic performance when operated with the new PWS and the existing Shack Hartmann wavefront sensor (SH WFS). The upgrade implementation and preliminary on-sky results are discussed. © 2019 AO4ELT 2019 - Proceedings 6th Adaptive Optics for Extremely Large Telescopes. All rights reserved

Methane line opacities in very cool stellar objects

Aims. We investigate the effects of different line data for methane 12CH4 on the structures of model atmospheres and low resolution synthetic spectra for ultra-cool substellar objects. Methods. For each set of methane line data we compare the resulting model atmospheres and spectra computed with the general purpose model atmosphere code PHOENIX. Results. The new HG

Ab initio modeling of molecular IR spectra of astrophysical interest: application to CH

Aims. We describe an ab initio-based numerical method of obtaining infrared spectroscopic data (line list) of polyatomic molecules that allows calculation of complete sets of lines for temperatures up to several thousand Kelvin. While the main focus is on completeness and consistency, not spectroscopic accuracy, the approach is in principle “exact” for line positions and, although not exact for line strengths, of sufficient accuracy to be of value, especially in wavelength regions where there are gaps in reliable experimental data. Methods. Global potential energy and dipole moment hypersurfaces are fitted to the results of ab initio electronic structure calculations. The MULTIMODE software is then used to obtain rovibrational energy levels and dipole transition matrix elements. This information is used to calculate a complete set of Einstein coefficients of spontaneous emission A ij. Results. The method is applied to obtain a spectroscopic database for methane containing over 1.4 million lines up to an upper state energy of 6200 cm-1 ($\sim$9000 K). The emission spectrum of CH4 at 1000 K is calculated with the complete set of Einstein coefficients and compared with the one obtained from the HITRAN database. Gaps in the database are realistically filled in by the calculated spectrum. Conclusions. Consistent and complete databases are important for astrophysical applications. Databases obtained by the method described here fulfill this requirement and are sufficiently accurate for astrophysical applications such as model atmosphere calculations and the corresponding synthetic spectra

Typing of inflammatory lesions of the pituitary

Inflammatory pituitary lesions account for 1.8% of all specimens from the German Pituitary Tumor Registry. They occure in 0.5% of the autoptical specimens and in 2.2% of the surgical cases. Women are significantly more often affected than men and are often younger when first diagnosed. In general, primary and secondary inflammation can be distinguished, with secondary types occurring more frequently (75.1%) than idiopathic inflammatory lesions (15.4%). In primary inflammation, the lymphocytic type is more common (88.5%) than the granulomatous type of hypophysitis (11.5%). The most common causes of secondary inflammation are Rathke's cleft cysts (48.6%), followed by tumors (17.4%) such as the craniopharyngioma (9.1%), adenoma (5.5%) or germinoma (2.0%). More causes are tumor-like lesions (7.1%) such as xanthogranuloma (3.5%) or Langerhans histiocytosis (3.5%), abscesses (5.5%), generalized infections (5.1%), spreaded inflammations (4.7%) and previous surgeries (4.0%). In 1.6% of all specimens the reason for the inflammation remains unclear. The described classification of hypophysitis is important for specific treatment planning after surgery