@article{15725, abstract = {{Adaptive kinetic Monte Carlo simulation (aKMC) is employed to study the dynamics and the diffusion of point defects in the CuInSe2 lattice. The aKMC results show that lighter alkali atoms can diffuse into the CuInSe2 grains, whereas the diffusion of heavier alkali atoms is limited to the Cu-poor region of the absorber. The key difference between the diffusion of lighter and heavier alkali elements is the energy barrier of the ion exchange between alkali interstitial atoms and Cu. For lighter alkali atoms like Na, the interstitial diffusion and the ion-exchange mechanism have comparable energy barriers. Therefore, Na interstitial atoms can diffuse into the grains and replace Cu atoms in the CuInSe2 lattice. In contrast to Na, the ion-exchange mechanism occurs spontaneously for heavier alkali atoms like Rb and the further diffusion of these atoms depends on the availability of Cu vacancies. The outdiffusion of alkali substitutional atoms from the grains results in the formation of Cu vacancies which in turn increases the hole concentration in the absorber. In this respect, Na is more efficient than Rb due to the higher concentration of Na substitutional defects in the CuInSe2 grains.}}, author = {{Kormath Madam Raghupathy, Ramya and Kühne, Thomas and Henkelman, Graeme and Mirhosseini, Hossein}}, issn = {{2513-0390}}, journal = {{Advanced Theory and Simulations}}, title = {{{Alkali Atoms Diffusion Mechanism in CuInSe 2 Explained by Kinetic Monte Carlo Simulations}}}, doi = {{10.1002/adts.201900036}}, year = {{2019}}, } @article{34303, author = {{Elgabarty, Hossam and Kaliannan, Naveen Kaliannan and Kühne, Thomas}}, issn = {{2045-2322}}, journal = {{Scientific Reports}}, keywords = {{Multidisciplinary}}, number = {{1}}, publisher = {{Springer Science and Business Media LLC}}, title = {{{Enhancement of the local asymmetry in the hydrogen bond network of liquid water by an ultrafast electric field pulse}}}, doi = {{10.1038/s41598-019-46449-5}}, volume = {{9}}, year = {{2019}}, } @article{21, abstract = {{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.}}, author = {{Richters, Dorothee and Lass, Michael and Walther, Andrea and Plessl, Christian and Kühne, Thomas}}, journal = {{Communications in Computational Physics}}, number = {{2}}, pages = {{564--585}}, publisher = {{Global Science Press}}, title = {{{A General Algorithm to Calculate the Inverse Principal p-th Root of Symmetric Positive Definite Matrices}}}, doi = {{10.4208/cicp.OA-2018-0053}}, volume = {{25}}, year = {{2019}}, } @article{20, abstract = {{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.}}, author = {{Lass, Michael and Kühne, Thomas and Plessl, Christian}}, issn = {{1943-0671}}, journal = {{Embedded Systems Letters}}, number = {{2}}, pages = {{ 33--36}}, publisher = {{IEEE}}, title = {{{Using Approximate Computing for the Calculation of Inverse Matrix p-th Roots}}}, doi = {{10.1109/LES.2017.2760923}}, volume = {{10}}, year = {{2018}}, } @article{13209, abstract = {{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.}}, author = {{Sahoo, Sudhir and Kormath Madam Raghupathy, Ramya and Kühne, Thomas and Mirhosseini, Hossein}}, journal = {{J. Phys. Chem. C}}, number = {{37}}, pages = {{21202--21209}}, title = {{{Theoretical Investigation of Interaction of CuInSe2 Absorber Material with Oxygen, Hydrogen, and Water}}}, doi = {{10.1021/acs.jpcc.8b06709}}, volume = {{122}}, year = {{2018}}, } @article{13210, abstract = {{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.}}, author = {{Kormath Madam Raghupathy, Ramya and Wiebeler, Hendrik and Kühne, Thomas and Felser, Claudia and Mirhosseini, Hossein}}, journal = {{Chemistry of Materials}}, number = {{19}}, pages = {{6794--6800}}, publisher = {{American Chemical Society}}, title = {{{Database screening of ternary chalcogenides for p-type transparent conductors}}}, doi = {{10.1021/acs.chemmater.8b02719}}, volume = {{30}}, year = {{2018}}, } @article{13208, abstract = {{In this work, high-throughput ab initio calculations are employed to identify the most promising chalcogenide-based semiconductors for p-type transparent conducting materials (TCMs). A large computational data set is investigated by data mining. Binary semiconductors with large band gaps (Eg) and anions that are less electronegative than oxygen are considered. The roles of intrinsic defects and extrinsic dopants are investigated to probe the p-type performance of these semiconductors. Nine novel p-type non-oxide TCMs that have a low hole effective mass, good optical transparency, and hole dopability are proposed (ZnS, ZnSe, ZnTe, MgS, MgTe, GaSe, GaTe, Al2Se3, and BeTe). This study also focuses on a material engineering approach to modulate the electronic properties as a function of the layer thickness and external stress.}}, author = {{Kormath Madam Raghupathy, Ramya and Kühne, Thomas and Felser, Claudia and Mirhosseini, Hossein}}, journal = {{Journal of Materials Chemistry C}}, number = {{3}}, pages = {{541--549}}, publisher = {{Royal Society of Chemistry}}, title = {{{Rational design of transparent p-type conducting non-oxide materials from high-throughput calculations}}}, doi = {{https://doi.org/10.1039/C7TC05311H }}, volume = {{6}}, year = {{2018}}, } @article{15727, author = {{Kodalle, Tim and Kormath Madam Raghupathy, Ramya and Bertram, Tobias and Maticiuc, Natalia and Yetkin, Hasan A. and Gunder, René and Schlatmann, Rutger and Kühne, Thomas and Kaufmann, Christian A. and Mirhosseini, S. Hossein}}, issn = {{1862-6254}}, journal = {{physica status solidi (RRL) – Rapid Research Letters}}, title = {{{Properties of Co‐Evaporated RbInSe 2 Thin Films}}}, doi = {{10.1002/pssr.201800564}}, year = {{2018}}, } @inproceedings{1590, abstract = {{We present the submatrix method, a highly parallelizable method for the approximate calculation of inverse p-th roots of large sparse symmetric matrices which are required in different scientific applications. Following the idea of Approximate Computing, we allow imprecision in the final result in order to utilize the sparsity of the input matrix and to allow massively parallel execution. For an n x n matrix, the proposed algorithm allows to distribute the calculations over n nodes with only little communication overhead. The result matrix exhibits the same sparsity pattern as the input matrix, allowing for efficient reuse of allocated data structures. We evaluate the algorithm with respect to the error that it introduces into calculated results, as well as its performance and scalability. We demonstrate that the error is relatively limited for well-conditioned matrices and that results are still valuable for error-resilient applications like preconditioning even for ill-conditioned matrices. We discuss the execution time and scaling of the algorithm on a theoretical level and present a distributed implementation of the algorithm using MPI and OpenMP. We demonstrate the scalability of this implementation by running it on a high-performance compute cluster comprised of 1024 CPU cores, showing a speedup of 665x compared to single-threaded execution.}}, author = {{Lass, Michael and Mohr, Stephan and Wiebeler, Hendrik and Kühne, Thomas and Plessl, Christian}}, booktitle = {{Proc. Platform for Advanced Scientific Computing (PASC) Conference}}, isbn = {{978-1-4503-5891-0/18/07}}, keywords = {{approximate computing, linear algebra, matrix inversion, matrix p-th roots, numeric algorithm, parallel computing}}, location = {{Basel, Switzerland}}, publisher = {{ACM}}, title = {{{A Massively Parallel Algorithm for the Approximate Calculation of Inverse p-th Roots of Large Sparse Matrices}}}, doi = {{10.1145/3218176.3218231}}, year = {{2018}}, } @inproceedings{169, abstract = {{We apply methods of genetic programming to a general problem from software engineering, namely example-based generation of specifications. In particular, we focus on model transformation by example. The definition and implementation of model transformations is a task frequently carried out by domain experts, hence, a (semi-)automatic approach is desirable. This application is challenging because the underlying search space has rich semantics, is high-dimensional, and unstructured. Hence, a computationally brute-force approach would be unscalable and potentially infeasible. To address that problem, we develop a sophisticated approach of designing complex mutation operators. We define ‘patterns’ for constructing mutation operators and report a successful case study. Furthermore, the code of the evolved model transformation is required to have high maintainability and extensibility, that is, the code should be easily readable by domain experts. We report an evaluation of this approach in a software engineering case study.}}, author = {{Kühne, Thomas and Hamann, Heiko and Arifulina, Svetlana and Engels, Gregor}}, booktitle = {{Proceedings of the 19th European Conference on Genetic Programming (EuroGP 2016)}}, pages = {{278----293}}, title = {{{Patterns for Constructing Mutation Operators: Limiting the Search Space in a Software Engineering Application}}}, doi = {{10.1007/978-3-319-30668-1_18}}, year = {{2016}}, } @article{15734, author = {{Ghorbani, Elaheh and Kiss, Janos and Mirhosseini, Hossein and Schmidt, Markus and Windeln, Johannes and Kühne, Thomas and Felser, Claudia}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, pages = {{2064--2069}}, title = {{{Insights into Intrinsic Defects and the Incorporation of Na and K in the Cu2ZnSnSe4 Thin-Film Solar Cell Material from Hybrid-Functional Calculations}}}, doi = {{10.1021/acs.jpcc.5b11022}}, year = {{2016}}, } @article{45766, author = {{John, Christopher and Spura, Thomas and Kühne, Thomas D.}}, journal = {{Phys. Rev. E}}, title = {{{Quantum ring-polymer contraction method: Including nuclear quantum effects at no additional computational cost in comparison to ab Initio molecular dynamics}}}, volume = {{93}}, year = {{2016}}, } @inproceedings{25, author = {{Lass, Michael and Kühne, Thomas and Plessl, Christian}}, booktitle = {{Workshop on Approximate Computing (AC)}}, title = {{{Using Approximate Computing in Scientific Codes}}}, year = {{2016}}, } @article{15736, author = {{Ghorbani, Elaheh and Kiss, Janos and Mirhosseini, Hossein and Roma, Guido and Schmidt, Markus and Windeln, Johannes and Kühne, Thomas and Felser, Claudia}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, pages = {{25197--25203}}, title = {{{Hybrid-Functional Calculations on the Incorporation of Na and K Impurities into the CuInSe2 and CuIn5Se8 Solar-Cell Materials}}}, doi = {{10.1021/acs.jpcc.5b07639}}, year = {{2015}}, } @article{34307, abstract = {{

“On-the-fly” coupled cluster-based path-integral molecular dynamics simulations predict that the effective potential of the protonated water–dimer has a single-well only.

}}, author = {{Spura, Thomas and Elgabarty, Hossam and Kühne, Thomas}}, issn = {{1463-9076}}, journal = {{Physical Chemistry Chemical Physics}}, keywords = {{Physical and Theoretical Chemistry, General Physics and Astronomy}}, number = {{22}}, pages = {{14355--14359}}, publisher = {{Royal Society of Chemistry (RSC)}}, title = {{{“On-the-fly” coupled cluster path-integral molecular dynamics: impact of nuclear quantum effects on the protonated water dimer}}}, doi = {{10.1039/c4cp05192k}}, volume = {{17}}, year = {{2015}}, } @article{34309, author = {{Kessler, Jan and Elgabarty, Hossam and Spura, Thomas and Karhan, Kristof and Partovi-Azar, Pouya and Hassanali, Ali A. and Kühne, Thomas}}, issn = {{1520-6106}}, journal = {{The Journal of Physical Chemistry B}}, keywords = {{Materials Chemistry, Surfaces, Coatings and Films, Physical and Theoretical Chemistry}}, number = {{31}}, pages = {{10079--10086}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Structure and Dynamics of the Instantaneous Water/Vapor Interface Revisited by Path-Integral and Ab Initio Molecular Dynamics Simulations}}}, doi = {{10.1021/acs.jpcb.5b04185}}, volume = {{119}}, year = {{2015}}, } @article{34308, author = {{Kühne, Thomas and Partovi-Azar, P. and Elgabarty, Hossam}}, issn = {{1439-9598}}, journal = {{Nachrichten aus der Chemie}}, keywords = {{General Chemical Engineering, General Chemistry}}, number = {{3}}, pages = {{327--335}}, publisher = {{Wiley}}, title = {{{Ab-initio-Moleküldynamik}}}, doi = {{10.1002/nadc.201590095}}, volume = {{63}}, year = {{2015}}, } @article{34310, author = {{Elgabarty, Hossam and Khaliullin, Rustam Z. and Kühne, Thomas D.}}, issn = {{2041-1723}}, journal = {{Nature Communications}}, keywords = {{General Physics and Astronomy, General Biochemistry, Genetics and Molecular Biology, General Chemistry}}, number = {{1}}, publisher = {{Springer Science and Business Media LLC}}, title = {{{Covalency of hydrogen bonds in liquid water can be probed by proton nuclear magnetic resonance experiments}}}, doi = {{10.1038/ncomms9318}}, volume = {{6}}, year = {{2015}}, } @article{45767, author = {{Calcavecchia, Francesco and Pederiva, Francesco and Kalos, Malvin H. and Kühne, Thomas D.}}, journal = {{Phys. Rev. E}}, title = {{{Sign problem of the fermionic shadow wave function}}}, volume = {{90}}, year = {{2014}}, } @article{45769, author = {{Kühne, Thomas D. and Khaliullin, Rustam Z.}}, journal = {{Nature Commun.}}, title = {{{Electronic signature of the instantaneous asymmetry in the first coordination shell of liquid water}}}, volume = {{4}}, year = {{2013}}, }