Liviu UNGUR

Liviu UNGUR

Assistant Professor

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Research

ORCID: 0000-0001-5015-4225
ResearcherID: G-2057-2012
Google Scholar: https://scholar.google.be/citations?user=Pn-zPAQAAAAJ

 

Recognition and Achievements

• Postdoctoral mandate of the Fonds Wetenschappelijk Onderzoek Vlaanderen (FWO)
• Best Doctoral Thesis in Molecular Magnetism, European Institute of Molecular Magnetism, June 2014

 

Research Interests

• quantum chemistry; electronic structure theory; ab initio calculations;
• crystal and ligand field models;
• theoretical description of electronic structure and properties (magnetic, optic) of lanthanide-, actinide-, transition metals compounds;
• single molecule magnets; magnetic relaxation;
• toroidal and non-collinear magnetization;
• weak intra- and inter- molecular interactions (e.g. exchange and magnetic interactions) and their description by quantum chemistry methods;

 

Research Highlight

1) Ab initio crystal field

A fully ab initio methodology is proposed for the extraction of the complete set of crystal field parameters defining the splitting of the ground J-multiplet of lanthanide complexes. It is shown that straightforward increase of computational effort (double 4f-shell included in the active space, dynamical correlation via XMS-CASPT2, etc.) leads to a significantly better description of the electronic spectrum and properties of the investigated Er-trensal compound. The electrostatic contributions to CF parameters in this complex, calculated with true charge distributions in the ligands, yield less than half of the total CF splitting, thus pointing to the dominant role of covalent effects. This analysis allows the conclusion that ab initio crystal field is an essential tool for the decent description of lanthanides.

2) Single-molecule magnets

Lanthanide-based single-molecule magnets are leading materials for achieving magnetization blocking at the level of one molecule. In this paper, we examine the physical requirements for efficient magnetization blocking in single-ion complexes and identify the design principles for achieving very high magnetization blocking barriers in lanthanide-based compounds. The key condition is the preponderant covalent binding of the Ln ion to one of the ligand atoms, tremendously enhancing the axial crystal field. We also make an overview of practical schemes for the implementation of this principle. These are (1) the effective lowering of the coordination number via displacement of the Ln ion to one of the atoms in the coordination polyhedron, (2) the design of two-coordinated complexes, and (3) the stabilization of diatomic compounds in cages and on surfaces. The last proposal is appealing in connection to spintronics applications, especially via the exploration of robust and highly anisotropic [LnX] units displaying multilevel blocking barriers of thousands of Kelvin and prospects for room-temperature magnetization blocking.

3) Non-collinear magnetism

Single-molecule toroics (SMTs) are defined, by analogy with single-molecule magnets, as bistable molecules with a toroidal magnetic state, and seem to be most promising for future applications in quantum computing and information storage and use as multiferroic materials with magnetoelectric effect. As an interdisciplinary research area that spans chemistry, physics and material sciences, synthetic chemists have produced systems suitable for detailed study by physicists and materials scientists, while ab initio calculations have been playing a major role in the detection of toroidal magnetization and the advancement of this field.

 

Teaching Contributions AY2022/2023

• CM2133 Foundations of Physical Chemistry
• CM5235 Applied Computational Chemistry

 

Representative Publications  

• Ungur, L.; Chibotaru, L. F.; Ab Initio Crystal Field for Lanthanides, Chem. Eur. J. 2017, 23, 3708-3718.
• Ungur, L.; Chibotaru, L. F.; Strategies toward High-Temperature Lanthanide-Based Single-Molecule Magnets, Inorg. Chem. 2016, 55, 10043-10056.
• Snyder, B. E. R.; Vanelderen, P.; Bols, M. L.; Hallaert, S. D.; Bottger, L. H.; Ungur, L.; Pierloot, K.; Schoonheydt, R. A.; Sels, B. F.; Solomon, E. I.; The active site of low-temperature methane hydroxylation in iron-containing zeolites, Nature 2016, 536, 317-321.
• Ungur, L.; Lin, S. Y.; Tang, J. K.; Chibotaru, L. F.; Single-molecule toroics in Ising-type lanthanide molecular clusters, Chem. Soc. Rev. 2014, 43, 6894-6905.
• Ungur, L.; Le Roy, J. J.; Korobkov, I.; Murugesu, M.; Chibotaru, L. F.; Fine-tuning the Local Symmetry to Attain Record Blocking Temperature and Magnetic Remanence in a Single-Ion Magnet, Angew. Chem. Int. Ed. 2014, 53, 4413-4417.
• Ungur, L.; Thewissen, M.; Costes, J. P.; Wernsdorfer, W.; Chibotaru, L. F.; Interplay of Strongly Anisotropic Metal Ions in Magnetic Blocking of Complexes, Inorg. Chem. 2013, 52, 6328-6337.
• Chibotaru, L. F.; Ungur, L.; Ab initio calculation of anisotropic magnetic properties of complexes. I. Unique definition of pseudospin Hamiltonians and their derivation, J. Chem. Phys. 2012, 137.
• Ungur, L.; Chibotaru, L. F.; Magnetic anisotropy in the excited states of low symmetry lanthanide complexes, Phys. Chem. Chem. Phys. 2011, 13, 20086-20090.
• Chibotaru, L. F.; Ungur, L.; Soncini, A.;The origin of nonmagnetic Kramers doublets in the ground state of dysprosium triangles: Evidence for a toroidal magnetic moment, Angew. Chem. Int. Ed. 2008, 47, 4126-4129.