Research

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Development of Green's function methods for electronic excitations & electron dynamics

GW is a Green's function methods and often regarded as state-of-the-art method to compute electronic band structures of solids. GW calculations are used to screen promising materials candidates for applications, or to calculate parameters for the use in models. Today's largest supercomputers are required?when applying GW to systems with more than hundred atoms in the simulation. Such large-scale calculations are used to model nanoscale molecules and materials with interfaces and defects, for example tailor-made graphene structures?used for all-carbon?electronics [1,2] or complex two-dimensional materials [3].

We work on a low-scaling GW algorithm [1,3,4] to enable GW calculations on thousands of atoms. The computational cost of GW can be reduced?to?O(N²), where N is the number of atoms in the simulation.?For two-dimensional materials, we have shown that low-scaling algorithms can reduce the computational cost by up to five orders of magnitude [3]. Our low-scaling GW algorithms are implemented in the widely used open-source package CP2K?and?have been highlighted in a community publication [5] and by the Gauss Center for Supercomputing.?

Our goal is to extend the low-scaling techniques to other electronic structure methods as the Bethe-Salpeter equation for excitons and to ultrafast electron dynamics.

We also apply our developed methods to pertinent problems in physics and chemistry, in close collaboration with experimental groups [2,6].

[1]? J. Wilhelm, D. Golze, L. Talirz, J. Hutter, C. A. Pignedoli: Toward GW calculations on thousands of atoms, J. Phys. Chem. Lett. 9, 306-312 (2018).

[2]? G. B. Barin, Q. Sun, J.?Wilhelm, P. Ruffieux et al.:?Growth optimization and device integration of narrow-bandgap graphene nanoribbons,?Small 18, 2202301 (2022).

[3] M. Graml, K. Zollner, D. Hernangomez-Perez, P. E. Faria Junior, J. Wilhelm, Low-scaling GW algorithm applied to transition-metal dichalcogenide heterobilayers, J. Chem. Theory Comput. 20, 2202 (2024).

[4]? J. Wilhelm, P. Seewald, D. Golze: Low-scaling GW with benchmark accuracy and application to phosphorene nanosheets, J. Chem. Theory Comput. 17, 1662 (2021).

[5]? T. D. Kühne, M. Iannuzzi,?J. Wilhelm, J. Hutter?et al.: CP2K: An electronic structure and molecular dynamics software package - Quickstep: Efficient and accurate electronic structure calculations, J. Chem. Phys. 152, 194103 (2020).?

[6]?J. Am. Chem. Soc. 140, 3532-3536 (2018),?J. Am. Chem. Soc. 141, 2843-2846 (2019),?Nat. Commun. 10, 861 (2019),?Nat. Chem. 14, 1061-1067 (2022)
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Ultrafast electron dynamics

Recent progress in laser technology made it possibl