Study On Phonon Mode And Magnetic Properties Of Osmium Oxide

The transition metal oxide of group 5d presents various peculiar physical characteristics in the exploration of scholars.The space group of Na Os O3 is Pnma(62)and the point group is mmm.In this paper,the four magnetic configurations G-AFM,A-AFM,C-AFM and NM are studied.WIEN2 k calculated the electronic structure of Na Os O3 under the density functional theory(DFT)and the allelectron full potential energy linear patch plus plane wave method.Our calculation result is that the magnetic moment on Os is 0.86?(33),which is slightly larger than the theoretical result of Wan et al.0.83?(33).Through the analysis of electron band diagram,density of state diagram,and partial density of state diagram,it is determined that G-AFM is the ground state of Na Os O3.Afterwards,Na Os O3 was studied in terms of phonons.The combination of VASP and density functional perturbation theory is used to calculate the four magnetic configurations of Na Os O3.The phonon spectrum,phonon density of state diagram,and partial density of state diagram of Na Os O3 with different magnetic configurations were obtained.The phonon spectrum has no virtual frequency and stable dynamics.The phonon vibration mode near the peak is also studied.Three vibration modes are selected near the peak,namely B3 u mode,B2 u mode and B1 g mode.In the low-frequency region,after adding the G-type antiferromagnetic,the B3 u mode moves to the high frequency,and slight signs of hardening appear.In the high frequency region,after adding the G-type antiferromagnetic,the B2 u mode moves to the low frequency,and slight signs of softening appear,and the B1 g mode hardens after adding G-type antiferromagnetic.The vibration intensity of each atom in the three vibration modes coincides with the contribution of each atom in the density of states.At point,there are a total of 60 vibration modes,with 3 acoustic branches and 57 optical branches.In addition,the B2 g,B3g,and Ag modes are also studied,and it was found that these three modes were hardened,which was consistent with the results of Calder et al.Pressure is the easiest way to change the properties of materials.When an object is pressed,the structure of the material will change phase.The calculation basis of this paper is the well-known firstprinciple,and then through the powerful structure prediction technology,the transition metal oxide Na Os O3 under different pressures is further explored.Using the USPEX evolutionary algorithm,for Na Os O3 under 50 GPa,100GPa,200 GPa,300GPa,and 400 GPa pressure,the structural prediction was carried out,and then the density functional theory combined with the VASP program method was used to geometrically optimize each structure.Then,the WEIN2 K program has use to calculate the band and electron density of state of Na Os O3 under high pressure,use phonopy to analyze the crystal under high pressure,and obtain the phonon spectrum of Na Os O3 under 400 GPa.Through USPEX search for the shape of Na Os O3 under high pressure,we found different structures,and then separately calculated the structures searched under high pressure.The phonon spectra of different structures are used to judge the stability of the structure.After a long period of phonon calculations,we found that there are three main stable structures of structures in Na Os O3.These types of structures are Pbcm structure,Pnma structure,and P63/mmc structure.Respectively,orthogonal structures,orthogonal structures,hexagonal structures.Finally,the stable structures of these three structures are calculated,and the phonon spectrum,density of state diagram,electron band diagram,and partial density of state diagram are obtained.Through analysis,it is found that Na Os O3 of the three structures are in the metallic state.