TY - JOUR AU - Kaliannan, Naveen Kumar AU - Henao Aristizabal, Andres AU - Wiebeler, Hendrik AU - Zysk, Frederik AU - Ohto, Tatsuhiko AU - Nagata, Yuki AU - D. Kühne, Thomas ID - 13232 JF - Molecular Physics TI - Impact of intermolecular vibrational coupling effects on the sum-frequency generation spectra of the water/air interface ER - TY - JOUR AU - Müller, Patrick AU - Neuba, Adam AU - Flörke, Ulrich AU - Henkel, Gerald AU - Kühne, Thomas D. AU - Bauer, Matthias ID - 13233 IS - 16 JF - The Journal of Physical Chemistry A TI - Experimental and Theoretical High Energy Resolution Hard X-ray Absorption and Emission Spectroscopy on Biomimetic Cu2S2 Complexes VL - 123 ER - TY - JOUR AB - Thermal treatment of hexaazatriphenylene-hexacarbonitrile (HAT-CN) in the temperature range from 500 °C to 700 °C leads to precise control over the degree of condensation{,} and thus atomic construction and porosity of the resulting C2N-type materials. Depending on the condensation temperature of HAT-CN{,} nitrogen contents of more than 30 at% can be reached. In general{,} these carbons show adsorption properties which are comparable to those known for zeolites but their pore size can be adjusted over a wider range. At condensation temperatures of 525 °C and below{,} the uptake of nitrogen gas remains negligible due to size exclusion{,} but the internal pores are large and polarizing enough that CO2 can still adsorb on part of the internal surface. This leads to surprisingly high CO2 adsorption capacities and isosteric heat of adsorption of up to 52 kJ mol−1. Theoretical calculations show that this high binding enthalpy arises from collective stabilization effects from the nitrogen atoms in the C2N layers surrounding the carbon atom in the CO2 molecule and from the electron acceptor properties of the carbon atoms from C2N which are in close proximity to the oxygen atoms in CO2. A true CO2 molecular sieving effect is achieved for the first time in such a metal-free organic material with zeolite-like properties{,} showing an IAST CO2/N2 selectivity of up to 121 at 298 K and a N2/CO2 ratio of 90/10 without notable changes in the CO2 adsorption properities over 80 cycles. AU - Walczak, Ralf AU - Savateev, Aleksandr AU - Heske, Julian Joachim AU - Tarakina, Nadezda V. AU - Sahoo, Sudhir AU - Epping, Jan D. AU - Kühne, Thomas AU - Kurpil, Bogdan AU - Antonietti, Markus AU - Oschatz, Martin ID - 13236 JF - Sustainable Energy Fuels TI - Controlling the strength of interaction between carbon dioxide and nitrogen-rich carbon materials by molecular design ER - TY - JOUR AU - Elgabarty, Hossam AU - Kaliannan, Naveen Kumar AU - Kühne, Thomas D. ID - 13237 JF - Scientific Reports TI - Enhancement of the asymmetry in the hydrogen bond network of liquid water by an ultrafast electric field pulse VL - 9 ER - TY - JOUR AB - The behavior of alkali atom point defects in polycrystalline CuInSe2 is studied. In this work, three grain boundary models, one coherent twin boundary and two twin boundaries with dislocation cores, are considered. Total energy calculations show that all alkali metals tend to segregate at the grain boundaries. In addition, the segregation of alkali atoms is more pronounced at the grain boundaries with the dislocation cores. The diffusion of alkali metals along and near grain boundaries is studied as well. The results show that the diffusion of alkali atoms in the grain boundary models is faster than within the bulk. In addition, the ion exchange between Na and Rb atoms at the grain boundaries leads to the Rb enrichment at the grain boundaries and the increase of the Na concentration in the bulk. While the effects of Na and Rb point defects on the electronic structure of the grain boundary with the anion-core dislocation are similar, Rb atoms passivate the grain boundary with the cation-core dislocation more effectively than Na. This can explain the further improvement of the solar cell performance after the RbF-postdeposition treatment. AU - Chugh, Manjusha AU - Kühne, Thomas D. AU - Mirhosseini, Hossein ID - 13230 IS - 16 JF - ACS Applied Materials & Interfaces TI - Diffusion of Alkali Metals in Polycrystalline CuInSe2 and Their Role in the Passivation of Grain Boundaries VL - 11 ER - TY - JOUR AB - We address the general mathematical problem of computing the inverse p-th root of a given matrix in an efficient way. A new method to construct iteration functions that allow calculating arbitrary p-th roots and their inverses of symmetric positive definite matrices is presented. We show that the order of convergence is at least quadratic and that adaptively adjusting a parameter q always leads to an even faster convergence. In this way, a better performance than with previously known iteration schemes is achieved. The efficiency of the iterative functions is demonstrated for various matrices with different densities, condition numbers and spectral radii. AU - Richters, Dorothee AU - Lass, Michael AU - Walther, Andrea AU - Plessl, Christian AU - Kühne, Thomas ID - 21 IS - 2 JF - Communications in Computational Physics TI - A General Algorithm to Calculate the Inverse Principal p-th Root of Symmetric Positive Definite Matrices VL - 25 ER - TY - JOUR AB - Approximate computing has shown to provide new ways to improve performance and power consumption of error-resilient applications. While many of these applications can be found in image processing, data classification or machine learning, we demonstrate its suitability to a problem from scientific computing. Utilizing the self-correcting behavior of iterative algorithms, we show that approximate computing can be applied to the calculation of inverse matrix p-th roots which are required in many applications in scientific computing. Results show great opportunities to reduce the computational effort and bandwidth required for the execution of the discussed algorithm, especially when targeting special accelerator hardware. AU - Lass, Michael AU - Kühne, Thomas AU - Plessl, Christian ID - 20 IS - 2 JF - Embedded Systems Letters SN - 1943-0663 TI - Using Approximate Computing for the Calculation of Inverse Matrix p-th Roots VL - 10 ER - TY - JOUR AB - We performed ab initio calculations to study oxygen and hydrogen point defects in the CuInSe2 (CISe) solar-cell material. We found that H interstitial defects (when one H atom is surrounded by four Se atoms) and HCu (when a H atom is replacing a Cu atom) are the most stable defects. Whereas these H substitutional defects remain neutral, H interstitial defects act as donor defects and are detrimental to the cell performance. The incorporation of H2 into the CISe lattice, on the other hand, is harmless to the p-type conductivity. Oxygen atoms tend to either substitute Se atoms in the CISe lattice or form interstitial defects, though the formation of substitutional defects is more favorable. All oxygen point defects have high formation energies, which results in a low concentration of these defects in CISe. However, the presence of oxygen in the system leads to the formation of secondary phases such as In2O3 and InCuO2. In addition to the point defects, we studied the adsorption of H2O molecules on a defect-free surface and a surface with a (2VCu + InCu) defect using the ab initio thermodynamics technique. Our results indicate that the dissociative water adsorption on the CISe surface is energetically unfavorable. Furthermore, in order to obtain a water-free surface, the surface with defects has to be calcined at a higher temperature compared to the defect-free surface. AU - Sahoo, Sudhir AU - Kormath Madam Raghupathy, Ramya AU - Kühne, Thomas AU - Mirhosseini, Hossein ID - 13209 IS - 37 JF - J. Phys. Chem. C TI - Theoretical Investigation of Interaction of CuInSe2 Absorber Material with Oxygen, Hydrogen, and Water VL - 122 ER - TY - JOUR AB - In this work, we investigated ternary chalcogenide semiconductors to identify promising p-type transparent conducting materials (TCMs). High-throughput calculations were employed to find the compounds that satisfies our screening criteria. Our screening strategy was based on the size of band gaps, the values of hole effective masses, and p-type dopability. Our search led to the identification of seven promising compounds (IrSbS, Ba2GeSe4, Ba2SiSe4, Ba(BSe3)2, VCu3S4, NbCu3Se4, and CuBS2) as potential TCM candidates. In addition, branch point energy and optical absorption spectra calculations support our findings. Our results open a new direction for the design and development of p-type TCMs. AU - Kormath Madam Raghupathy, Ramya AU - Wiebeler, Hendrik AU - Kühne, Thomas AU - Felser, Claudia AU - Mirhosseini, Hossein ID - 13210 IS - 19 JF - Chemistry of Materials TI - Database screening of ternary chalcogenides for p-type transparent conductors VL - 30 ER - TY - JOUR AU - Müller, Patrick AU - Karhan, Kristof AU - Krack, Matthias AU - Gerstmann, Uwe AU - Schmidt, Wolf Gero AU - Bauer, Matthias AU - Kühne, Thomas D. ID - 13405 JF - Journal of Computational Chemistry SN - 0192-8651 TI - Impact of finite-temperature and condensed-phase effects on theoretical X-ray absorption spectra of transition metal complexes ER -