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MM: Fachverband Metall- und Materialphysik

MM 41: Computational Materials Modelling - Solids and Molecules (joint session MM/CPP)

MM 41.3: Vortrag

Mittwoch, 18. März 2020, 16:15–16:30, IFW B

First-principles description of phase transitions in solids with rotating molecules and diffusing atoms — •Sergei Simak — IFM, Linköping University, Sweden

Solids with rotating molecules and diffusing atoms are examples of dynamically disordered phases of materials with great potential for applications, from fuel cells to optoelectronics. Description of thermodynamics of these materials is a challenge, as standard methods, like static phonon calculations fail due to the large displacements of atoms or the absence of well-defined equilibrium atomic positions. We briefly outline a method that offers a solution to the problem based on a stress-strain thermodynamic integration [1]. An example of lithium carbide, a fascinating material that combines strong covalent and weak ionic bonding resulting in a wide range of unusual properties, is considered [2]. The mechanism of its phase transition from the ground-state orthorhombic to the high-temperature cubic crystal, which is subject to both rotations of C-C dumbbells and Li self-diffusion, is revealed, and the thermodynamics is described.
[1] J. Klarbring and S. I. Simak, Phys. Rev. Lett. 121, 225702 (2018).
[2] S. Filippov, J. Klarbring, U. Häussermann, and S. I. Simak, Phys. Rev. Materials 3, 023602 (2019).