Mechanical and vibrational stability analysis on YbFe2As2 nanocrystal

In this thesis study, the possible ground states of YbFe2As2 nanocrystals were computationally investigated using the quantum chemistry-based VASP package program. Numerous structures were examined in a 1-2-2 stoichiometry for this compound where the high-temperature single-crystal experimental and theoretical studies have been reported to be in a monoclinic phase. The Density Functional Theory (DFT) based standard Generalized Gradient Approximation (GGA) was employed in the investigations. The exchange-correlation contribution was considered using the Perdew-Burke-Enzerhof (PBE) parameterization. The calculations revealed that the titled crystal could be mechanically and vibrationally stable in 7 different phases. The second-order elastic constants (Cij) and phonon dispersions, determined through the Strain-Stress method and Density Functional Perturbation Theory, were analyzed to confirm the stabilities. Mechanical moduli (bulk modulus, shear modulus, Young's modulus, Poisson's ratio, Debye temperature, and ambient sound velocities) and Vickers hardness parameters of the compound in the discovered phases were computed and interpreted. Additionally, room temperature heat capacities and fundamental vibration modes were obtained. The findings were compared with existing experimental and theoretical data.