Research interests

• Computational Methods: We use mostly, density-functional-theory based software, such as VASP, Quantum Espresso, and AIMS for electronic structure calculations. Depending on the scope of a project, we are also using classical potential software such as GULP and lammps.


• Materials Informatics and Materials Design: We extract and process online materials database content, as for example provided by AFLOW, and Materials Project in combination with physics and chemistry derived materials/property relations to pre-screen compounds and guide our search for new materials with desired functionalities.


• Magnetism: We are interested in collinear magnetism, to understand the principal of magnetic structures, and often augment these insights with spin-orbit couled computations to gain insights into magnetic anisotropy, assisted by Hubbard-U, to improve the description of the electronic and magnetic structure of open-shell paramagnetic elements. As part of our computational protocols we are also interested in the effects of symmetry breaking, that allows for the generation of a (small amount) of spontaneous polarization, leading to multiferroic behavior.


• Defects: Our interest in chemical defects originated from fuel cell research, where defect engineering is used to reduce the platinum dependence. We investigated various TMxNy (TM=Fe, Co, Ni) defect motifs embedded in a graphene matrix, to better understand (electro)catalytic aspects of these defects and their stability. Almost be default these defects break the symmetry and may be effective vehicles to promote symmetry breaking of host materials, enabling hew materials behavior.


• Quantum Enabled Materials and Quantum Computing: This interest may not be a surprise, seeing that the other research interests are also related to symmetry, and symmetry breaking. Here we are interested in bulk and 2D systems, and their effectiveness for band inversion and the formation of topologically protected electronic states, in the vicinity of the Fermi-level. At present we investigate strain as an efficient vehicle to induce topological behavior, in bulk and on surfaces. These materials are of great interest for several reasons:
  • Energy Technologies: the point-like vertex of the typical cone-like topological features in the electronic structure, corresponds to an extended wave function in real space, implying exceedingly high electrical conductivites and minimizing transport losses.
  • Quantum Computing: the superposition principle of quantum mechanics states that unless measured, the system is in a hybrid state of all possible states. This is rather impressive since it implies that the wave function contains all possible knowledge of the system, completely opposite to classical systems. The challenge is to stabilize the this wave function to temperatures at temperatures higher than milli Kelvin, such that the cooling cost for a quantum computer is reduced. Remembering that high-Tc superconductors currently do not operate at room temperature, shows the enormity of the challenges. However, a more modest goal is to raise operating temperatures above liquid nitrogen temperatures.
  Therefore, a better understanding of quantum behavior, its properties and how to overcome its fragile nature has significant potential to enable new technologies that are needed to address and master societal challenges such as energy security to information processing.


• Crystallography: Molecular water can be accommodated in materials either as part of the framework, or in intermittent void spaces. We focus on the intercrystalline water in void spaces. In order for intercrystalline water to be present (leaving kinetic aspects aside), there must be a favorable interaction between the water molecules and the framework. It is precisely through these interactions that hydrated minerals may show a different properties as compared to their anhydrous counterparts. Some examples are that water can affect the thermodynamic stability of materials, it has been reported that exposure to water can affect the efficiency of high-performance organic-inorganic hybrid perovskite solar cells, and it proces a mechanism for superprotonic chagre transport, that is directly relevant to fuel cells and membranes.
  
  Unfortunately, light elements are difficult to locate through standard neutron, and X-ray diffraction techniques, and the crystallography of water bearing minerals often remains incomplete. For this reason, we recently developed a point charge electrostatic model, TORQUE, to identify orientational equilibria in complex materials. We have applied TORQUE to urianium bearing minerals, curite, and vyacheslavite.
  
  Our current computing protocol benefits from the speed of TORQUE: typically, we identify rotational equilibria for 500-1000 random initial water orienations. Runtimes depend on the number of water molecules, but a recent example shows that for a unitcell with 352 atoms (including 64 water molecules), it took on average ~20 minutes per optimization. The frequency analysis of the equilibria shows that only 54 topologically distinct structures occur, that can be generate out of 23 distinct local orientations, promoting static disorder of the water array, an effect that contributes to the experimental challenges to resolve the complete crystal structure, including hydrogen, as bound to intercrystalline water.
  
  We are intrested in applying TORQUE to complete the water crystallography of more materials. At present we are focusing on uranium bearing minerals.

If you are interested in more details, please do not hesitate to reach out to Dr. Boris Kiefer.