Our group works in the development and application of state-of-the-art ab-initio methods to systems
of both fundamental and technological interest.
Until 2014 the group was located at the
Institut Lumière Matière,
situated at the Université Claude Bernard Lyon 1,
in Lyon, France.
From 2014 to 2023 we were at the Institut
für Physik of the Martin-Luther-Universität
Halle-Wittenberg.
Since 2023 we belong to the Research Center Future Energy Materials and Systems,
Faculty of Mechanical Engineering,
Ruhr University Bochum We are also sponsored by the following institutions: |

# Highlights (all highlights)

April 05, 2023

## Group moved to the Ruhr University Bochum

As of 01.04.2023, the group has moved to the Ruhr University Bochum, and will be located at the Centre for Interface-Dominated High Performance Materials (ZGH).

The press release can be found here.

July 12, 2021

## Two-dimensional binary metal-oxide quasicrystal approximants

We investigated, using a systematic computational approach, the possibility of the existence of two-dimensional quasicrystalline phases of binary metal-oxides. Our approach relied on the construction of the complete two-dimensional binary phase diagram through the use of unbiased global structural prediction methods. We then identified, in the low-energy periodic phases, structural elements that can be used to generate quasicrystalline phases through an inflation process. In this way we obtained chemically consistent two-dimensional quasicrystal approximants of both barium and titanium oxides. In the proposed structures, the metallic sites occupy the vertices of the aperiodic square-triangle tiling, while the oxygen atoms decorate the interior of the polygons. We then studied the properties of the approximants, both free-standing and deposited on a metallic substrate. Finally, we discussed in which circumstances the formation of these phases seems to be favored.
This work was just published in 2D Mater..

May 31, 2021

## Atomically Thin Pythagorean Tilings in Two Dimensions

We performied a theoretical study of an atomically thin, two-dimensional layer obtained by positioning atoms at the vertices of the classical Pythagorean tiling. This leads to an unusual geometrical pattern that is only stable for the three halogens Cl, Br, and I. In this Pythagorean structure, halogen atoms are arranged in strongly bound diatomic units that bind together by weaker electrostatic bonds. The energy of these phases is competitive with those of the low-temperature phase of the halogens and the two-dimensional layer obtained by exfoliating it. The Pythagorean layers are semiconducting, with an unusual band structure composed of very mobile holes and extremely heavy electrons. They are also soft, exhibiting small values of the elastic constants and a very low energy flexural mode. Analysis of the allowed Raman transitions reveals breathing-like modes that might be used to fingerprint, experimentally, the Pythagorean structure. Finally, we presented a series of substrates that, due to lattice matching and compatible symmetry, can be used to stabilize these peculiar two-dimensional layers.
This work has just been published in the J. Phys. Chem. Lett..

November 17, 2020

## Finding new crystalline compounds using chemical similarity

We proposed an efficient high-throughput scheme for the discovery of new stable crystalline phases. Our approach is based on the transmutation of known compounds, through the substitution of atoms in the crystal structure with chemically similar ones. The concept of similarity is defined quantitatively using a measure of chemical replaceability, extracted by data mining experimental databases. In this way we built 189981 possible crystal phases, including 18479 that are on the convex hull of stability. The resulting success rate of 9.72% is at least one order of magnitude better than the usual success rate of systematic high-throughput calculations for a specific family of materials, and comparable with speed-up factors of machine learning filtering procedures. As a first characterization of the set of 18479 new stable compounds, we calculated their electronic band gaps, magnetic moments, and hardness. Our approach, that can be used as a filter on top of any high-throughput scheme, enabled us to efficiently extract stable compounds from tremendously large initial sets, without any initial assumption on their crystal structures or chemical compositions.
This work has just been accepted in NPJ Comput. Mater.. Structural data can be downloaded from here.

February 04, 2019

## Special issue in honor of Eberhard K.U. Gross for his 65th birthday

With this special issue of the European Physical Journal B we pay homage to the scientific career of Eberhard Kurt Ulrich (Hardy) Gross, on occasion of his 65th birthday. Hardy is one of the most influential researchers in the field of theoretical density functional theory (DFT). His significant contributions started early, already as a student of Reiner Dreizler in Frankfurt and as a post-doc with the Nobel prize laureate Walter Kohn. In those years, Hardy Gross contributed to the birth of time-dependent density functional theory (TDDFT), DFT for superconductors, ensemble DFT, etc. Later, he was interested in other topics of electronic structure theory. This issue contains original contributions with topics close to Hardy’s heart (some of them already mentioned above),and is a mixture of colloquium and research papers.
This special issue has just been published in the Eur. Phys. J. B.

February 20, 2018

## Local hybrid density functional for interfaces

Hybrid functionals in density functional theory are becoming the state-of-the-art for the calculation of electronic properties of solids. The key of their performance is the way in which an amount of Fock exchange is mixed with semi-local exchange-correlation functionals. We propose here a local mixing dependent on the density alone, extending the results of a previously reported functional [Phys. Rev. B **83**, 035119 (2011)] to enable accurate calculations for interfaces and nanostructures. We verify that this hybrid functional has the potential to yield results of comparable quality as *GW* for band alignments and defects energy levels at interfaces, at the reduced cost of a hybrid density functional. This is possible as the form of the mixing is derived from *GW* theory, accounting for the electronic screening through its dependence on a density estimator of the local dielectric function. In contrast with other recent self-consistent schemes for the mixing parameter, our approach does not require to calculate the dielectric function and therefore it leads to a negligible increase of the computation time.
This work has just been accepted in J. Chem. Theory Comput..