scholarly journals Determination of Formation Energies and Phase Diagrams of Transition Metal Oxides with DFT+U

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4303
Author(s):  
Daniel Mutter ◽  
Daniel F. Urban ◽  
Christian Elsässer

Knowledge about the formation energies of compounds is essential to derive phase diagrams of multicomponent phases with respect to elemental reservoirs. The determination of formation energies using common (semi-)local exchange-correlation approximations of the density functional theory (DFT) exhibits well-known systematic errors if applied to oxide compounds containing transition metal elements. In this work, we generalize, reevaluate, and discuss a set of approaches proposed and widely applied in the literature to correct for errors arising from the over-binding of the O2 molecule and from correlation effects of electrons in localized transition-metal orbitals. The DFT+U method is exemplarily applied to iron oxide compounds, and a procedure is presented to obtain the U values, which lead to formation energies and electronic band gaps comparable to the experimental values. Using such corrected formation energies, we derive the phase diagrams for LaFeO3, Li5FeO4, and NaFeO2, which are promising materials for energy conversion and storage devices. A scheme is presented to transform the variables of the phase diagrams from the chemical potentials of elemental phases to those of precursor compounds of a solid-state reaction, which represents the experimental synthesis process more appropriately. The discussed workflow of the methods can directly be applied to other transition metal oxides.

Author(s):  
Daniel Mutter ◽  
Daniel F. Urban ◽  
Christian Elsässer

Knowledge about the formation energies of compounds is essential to derive phase diagrams of multi-component phases with respect to elemental reservoirs. The determination of formation energies using common (semi-)local exchange-correlation approximations of density functional theory (DFT) exhibits well-known systematic errors if applied to oxide compounds containing transition metal elements. In this work, we generalize, reevaluate and discuss a set of approaches proposed and widely applied in the literature to correct for errors arising from the over-binding of the O2 molecule and from correlation effects of electrons in localized transition-metal orbitals. The DFT+U method is exemplarily applied to iron oxide compounds, and a procedure is presented to obtain U values, which lead to formation energies and electronic band gaps comparable to experimental values. Using such corrected formation energies, we derive the phase diagrams for LaFeO3, Li5FeO4 and NaFeO2, which are promising materials for energy conversion and storage devices. A scheme is presented to transform the variables of the phase diagrams from the chemical potentials of elemental phases to those of precursor compounds of a solid-state reaction, which represents the experimental synthesis process more appropriately. The discussed workflow of methods can directly be applied to other transition metal oxides.


2004 ◽  
Vol 835 ◽  
Author(s):  
S. P. Singh ◽  
M. Tomar ◽  
Yasuyuki Ishikawa ◽  
S. B. Majumder ◽  
R. S. Katiyar

AbstractAverage Li intercalation potentials were calculated for lithium-4d-transition-metal-oxides. The effect on the intercalation voltage of metal substitution was systematically studied by altering the 4d transitional metals M (M= Mo, Nb, Rh, Zr, Ru) in LiMO2 in the α-NaFeO2 structure. Lattice parameters in the layered α-NaFeO2 structure computed in the GGA approximation are in reasonable agreement with experiment. The intercalation potentials and relative formation energies of the fully lithiated LiNi1/3Mn1/3Mo1/3O2, fully delithiated Ni1/3Mn1/3Mo1/3O2 and the intermediate phases, Li1/3Ni1/3Mn1/3Mo1/3O2 and Li2/3Ni1/3Mn1/3Mo1/3O2, were computed by employing a generalized alloy theory. A minute substitution of cationic Mo in LiNiMnO2 was experimentally investigated to examine the effect of the Mo substitution on the electrochemical properties.


2009 ◽  
Vol 16 (04) ◽  
pp. 525-532
Author(s):  
ZI-RONG TANG

The viability of facile oxidation and cycloaddition of fullerene C 60 with ruthenium tetraoxide ( RuO 4) has been confirmed by means of density functional theory calculations. Owing to the powerful capability of RuO 4 as an oxidant, the addition process has been found to occur readily in the absence of organic base as a catalyst, which is in remarkable contrast to the base-catalyzed osmylation of C 60 with osmium tetraoxide ( OsO 4). Significantly, we have found that boron can be employed as an effective promoter for enhancing the cycloaddition and complexation of transition metal oxides, e.g. RuO 4 and OsO 4, with C 60, in which the base is not needed at all. Our results suggest that boron doping into the lattice of fullerenes and carbon nanotubes would provide a well-defined approach for anchoring transition metal oxides.


2014 ◽  
Vol 28 (29) ◽  
pp. 1450205 ◽  
Author(s):  
Aytaç Erkişi ◽  
Erdem Kamil Yıldırım ◽  
Gökhan Gökoğlu

We present the electronic, magnetic and structural properties of the magnetic transition metal oxides PbMO 3 (M = Fe , Co , Ni ) in cubic perovskite structure. The calculations are based on the density functional theory (DFT) within plane-wave pseudopotential method and local spin density approximation (LSDA) of the exchange-correlation functional. On-site Coulomb interaction is also included in calculations (LSDA+ U ). The systems are considered in ferromagnetic (FM) and G-type antiferromagnetic (G-AFM) order. FM structures are energetically more favored than G-AFM and than non-magnetic states for all the systems studied. The spin-polarized electronic band structures show that all the structures have metallic property in FM order without Hubbard-U interaction (U eff = 0). However, the inclusion of on-site Coulomb interaction (U eff = 7 eV ) opens a semiconducting gap for majority spin channel of PbFeO 3 and of PbNiO 3 resulting in a half-metallic character. PbCoO 3 system remains as metallic with LSDA+ U scheme. Bonding features of all structures are largely determined by the hybridizations between O–p and d-states of transition metal atoms. The partial magnetic moment of Fe atom in PbFeO 3 is enhanced by inclusion of Hubbard-U interaction (2.55 μB ⇒ 3.78 μB). Total magnetic moments of half-metallic PbFeO 3 and of PbNiO 3 compounds are very close to integer values.


2015 ◽  
Vol 34 (5) ◽  
Author(s):  
Zbigniew Grzesik

AbstractIn the present paper the theoretical basis and experimental verification of a method, enabling the calculation of defect concentration and their mobility in transition metal oxides and sulphides have been described. The idea of proposed method consists in determination of both these parameters in indirect way, i.e. in studying the influence of aliovalent metallic additions on the oxidation kinetics of a given metal (doping effect). It has been shown that from the results of oxidation kinetics of binary alloys, the enthalpy and entropy of defect formation and their migration can be calculated. These data, in turn, can be used for the calculation of defect concentration and defect mobility in pure, undoped oxides. Such a possibility has been illustrated on the example of nonstoichiometric nickel oxide, Ni


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