First Principles Study of CaFe2As2 "Collapse" Under Pressure

Abstract

We perform first principles calculations on CaFe2As2 under hydrostatic pressure. Our total energy calculations show that though the striped antiferromagnetic (AFM) orthorhombic (OR) phase is favored at P=0, a non-magnetic collapsed tetragonal (cT) phase with diminished c-parameter is favored for P > 0.36 GPa, in agreement with experiments. Rather than a mechanical instability, this is an enthalpically driven transition from the higher volume OR phase to the lower volume cT phase. Calculations of electronic density of states reveal pseudogaps in both OR and cT phases, though As(p) hybridization with Fe(d) is more pronounced in the OR phase. We provide an estimate for the inter-planar magnetic coupling. Phonon entropy considerations provide an interpretation of the finite temperature phase boundaries of the cT phase.

4 pages, 4 figures, 1 Table

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• Lifshitz Transitions in 122-Pnictides Under Pressure
• First-principles study of the electronic structure of CaKRu${}_4$P${}_4$
• Observation of the Dirac Dispersions in Co-doped CaFe2As2