Predicted dynamically stable new phase for CrO2 compound: DFT + U calculations

Abstract

The structural, vibrational, elastic, mechanical, thermodynamic and magnetic properties of CrO2 compound in different phases have been studied using first-principles calculations based on density functional theory. Because of the presence of strong on-site Coulomb repulsion between the highly localized 3d electrons of Cr atoms, we have used GGA-PBEsol + U approach for the exchange-correlation energy and potential to get accurate results in the present study. From the various phases cubic (Pa3¯ and Fm3¯m), tetragonal (P42/m, P42/mnm, and P42/nmc), monoclinic (P21/c and Pca21), and orthorhombic (Pnnm, Pbcn, Pbca, and Pnma) of the CrO2 compound considered, we obtained that the P42/mnm phase is the lowest energies configuration as a function of volume. Our calculations lead to the following transitions, from P42/mnm phase → Pnnm phase (Pt = 14 GPa), Pnnm phase → Pbcn phase (Pt = 35 GPa), Pbcn phase → Pa3¯ phase (Pt = 46 GPa), Pa3¯ phase → Fm3¯m phase (Pt = 63 GPa), and from Fm3¯m phase → Pnma phase (Pt = 143 GPa). The calculated elastic properties for theP42/mnm, Pnnm, Pbcn,Pa3¯ and Fm3¯m phases showed that they are elastically stable. Considering the phonon dynamics of the CrO2 compound in the P42/mnm, Pnnm, Pbcn,Pa3¯, Fm3¯m phases, we observed that CrO2 compound is dynamically stable in all these phases. From electronic density of states calculations, we have found that CrO2 compound is half-metallic (HM) in the P42/mnm, Pnnm, Pbcn,Pa3¯ phases, and presents a half-semiconducting (HSC) behavior in the Fm3¯m phase. The HM and magnetic character found in CrO2 compound is attributed to the presence of spin polarized 3d orbitals of the chromium atoms. We have demonstrated through the electronic density of states (DOS), that the half-metallicity is preserved during transitions with magnetic moment of 2 μB per formula unit.