Back to search

FRINATEK-Fri prosj.st. mat.,naturv.,tek

First-principles modeling of magnetic topological materials from relativistic hybrid density functional theory

Alternative title: Modellering av magnetiske topologiske materialer ved bruk av relativistisk hybrid tetthetsfunksjonalteori fra første prinsipper

Awarded: NOK 3.4 mill.

Topological materials form a class of materials that exhibit remarkable properties protected by symmetries of fundamental physical laws. For instance, topological insulators conduct electricity only on their surface, while the "inside" of the material is insulating. Due to the symmetry protection, the electronic states that enable the surface conduction of electricity are immune to impurities found in natural samples. Such properties often originate in the coupling of the electron's spin with its orbital motion. This so-called spin-orbit coupling is a consequence of quantum mechanics combined with the Einstein's special theory relativity, and is significantly enhanced for materials containing heavy elements, such as tin, tungsten, gold, or mercury. Theoretically predicting and identifying potential topological materials requires solving complicated quantum mechanical equations using supercomputers. A description that is consistent with relativity and includes the spin-orbit coupling poses additional challenges to the theoretical models and needs much more computational time. MagneToMat targets topological properties of materials with an ordered arrangement of magnetic spins, called magnetic materials. These materials offer many practical applications, for example, as components of quantum computers, as memory devices with high density of information storage, and in controlling magnetic states with currents. The goal of MagneToMat is to deliver a reliable and efficient method that enables systematic studies of novel material properties and predictions of new magnetic solids from first principles. The project's objectives will be carried out in cooperation with Prof. A. Bansil and his group in Boston that has a strong expertise in modeling topological materials and an extensive network of collaborators among the theoretical and experimental groups. The project activities include developing tools for analyzing effects of the spin-orbit coupling in solids and applying the tools in the search for new promising materials. The project has lead to a number of results and novel methods that were published in renowned international scientific journals. I developed a method for calculating topological properties of two-dimensional (2D) materials using accurate and efficient approaches known in quantum chemistry that include full relativistic description of all electrons. Together with the host group of the outgoing phase, we investigated materials that are most promising in the field of spintronics due the properties originating from the strong spin-orbit-coupling in molybdenum and tungsten. We found, that contrary to the common belief in the community of quantum chemists, it is possible to reach systematic improvement of results with respect to the basis size and avoid the collapse of the numerical procedure if approaches developed here are used. This opens doors to studies of more advanced properties (related to magnetism in materials and relativistic effects) without the concern that the so-obtained results are of insufficient quality. I presented this research in the form of a poster and was invited to deliver talks on large international conferences reaching communities of both physicists and chemists dedicated to studies of relativistic effects in heavy elements. Furthermore, the methods developed for this project allowed us to study relativistic effects and a possible use of two complicated solid-state compounds as anodes and cathodes in Li-ion batteries. We investigated a material known as "Humboldtine" as a promising candidate for anodes and found that it reaches best electrochemical stability when fully dehydrated (water molecules are absent). For the cathode candidate, we focused on an iron-containing metal-organic framework. Our approach allowed us to gain microscopic understanding of the effect of structural distortions on the performance of this material in batteries. I transferred the knowledge to the Norwegian host institution (UiT) by delivering a series of seminars on material modelling where the knowhow acquired abroad at the Northeastern University was disseminated for the domestic audience. Furthermore, I continued collaborating on multiple projects tied to UiT and the Hylleraas Centre of Excellence. This included developing a relativistic extension to the theory of non-equilibrium ``pump-probe'' spectroscopy where two light pulses are used to study ultrafast attosecond electron dynamics. Ongoing and future work includes developing methods that enable theoretical predictions of spin defect qubits in 2D materials containing heavy metals. Accurate description of the magnetic interactions arising from the defects is important for determining how long the qubit can "live" before being damaged by the environment. For this purpose, the expertise of the Norwegian host in such simulations can be combined with the knowledge of material modelling of the abroad group.

The project has succeeded in bridging the methods developed by the theoretical chemistry community to study molecular systems with applications in computational condensed matter physics and material science. In particular, the ability to systematically improve the results and converge with respect to the one-electron orbital basis sets had not been achieved by the methods of quantum chemistry applied to solid-state systems before the implementation of this project. This result was disseminated among relevant scientific audiences that have shown interest in using the developed methods and tools. In addition, the accurate treatment of the electronic structure together with the capability of this approach to probe electronic density near nuclei in solids where the relativistic effects are strongest sparked interest of material scientists that work on engineering spin defects in 2D materials for the purpose of designing qubits with long decoherence times and spintronic devices. The international link established with the abroad host group within this project allows for a unique combination of expertise in theoretical material modelling, experimental material characterization techniques, and development of first-principles methods and tools for high-throughput material searches. The project has thus laid foundations for future collaborations with the potential to impact the design of technological applications in spintronic devices and quantum computing.

Reliable theoretical predictions of new materials and their properties depend on methods based on first principles. Such approaches aim to solve fundamental quantum mechanical equations and are free of undetermined model parameters. Topological materials exhibit a large variety of novel properties, with many possible applications in spintronics and quantum computing. However, majority of first-principles modeling of such properties has been performed on non-magnetic materials. This is due to significant challenges that arise in the theoretical descriptions of such materials. Topological materials often contain heavy elements, and thus their electronic structure requires a full relativistic treatment that incorporates effects of special theory of relativity. Within the relativistic framework, the spin and orbital degrees of freedom of an electron are coupled, which significantly increases the methodological complexity and computational cost. Magnetic materials pose further challenges to the methods due to large demands on the (magnetic) unit cell size, as well as limitations introduced by density functional theory. Hence, topological properties of realistic materials containing heavy elements remain largely unexplored. The MagneToMat project aims to solve both these challenges by formulating and implementing a relativistic first-principles theory based on a local atom-centered basis (Gaussian-type orbitals) and extending density functional theory to include hybrid functionals containing a portion of multicomponent exact exchange interaction. Within the scope of this project, the developed method will be applied to explore new two- and three-dimensional magnetic materials and their properties. The findings of this projects can be used to understand realistic solids and guide experiment in growing new samples.

Publications from Cristin

No publications found

No publications found

No publications found

Funding scheme:

FRINATEK-Fri prosj.st. mat.,naturv.,tek