Hybrid-Density Functional Calculations of Structural, Electronic, Magnetic, and Thermodynamic Properties of α-Cu2P2O7

We present a comparative study (using PBE, PBE0, and HSE functionals) of electronic and atomic structure, magnetism, and phonon dispersion relations of α-Cu2P2O7. Four possible magnetic configurations are considered, FM, AFM-1, AFM-2, and AFM-3. The calculations reveal that α-Cu2P2O7 is mechanically and thermodynamically stable. The elastic moduli indicate a weak resistance of the compound to volume and shear deformations. The electronic structure at the valence band maximum is dominated by O, with a small admixture of Cu-dx2−y2 states. The conduction band results from the hybridization between Cu and O states which, in the case of AFM-2, produces the largest band gap of 3.966 eV and the smallest magnetic moment of ±0.785 μB on Cu. AFM-2 is found to be the lowest-energy structure that may be viewed as consisting of quasi-one-dimensional −Cu1−Cu2−Cu3−Cu4− chains along the b axis; the antiferromagnetism is due to two identical Cu−O−Cu paths with a bond angle of 100.301∘. The phonon spectra exhibit four distinct frequency ranges corresponding to different vibrational modes of ions and ionic groups. Thus, a quantitative description of the structural, electronic, and magnetic properties of α-Cu2P2O7 is possible using the HSE hybrid functional, which enables computational studies of transition metal pyro compounds.