By the first-principles calculations, most studies indicated that the （1102）-CoO2 termination of LaCoO3 cannot be stabilized, which disagrees with the experimental observation. Besides the crystal structure, we foun...By the first-principles calculations, most studies indicated that the （1102）-CoO2 termination of LaCoO3 cannot be stabilized, which disagrees with the experimental observation. Besides the crystal structure, we found that the spin states of Co3＋ ions could affect surface stability, which previously were not well considered. By examining the different states of Co3＋ ions in hexagonal-phase LaCoO3, including low spin, intermediate spin, and high spin states, the surface grand potentials of these facets are calculated and compared. The results show that the spin states of Co3＋ ions have an important influence on stability of the LaCoO3 facets. Different from the previous results, the stability diagrams demonstrate that the （1102）- CoO2 termination can stably exist under O-rich condition, which can get an agreement with the experimental ones. Furthermore, the surface oxygen vacancy formation energies （Eov） of stable facets are computed in different spin states. The Eov of these possible exposed terminations strongly depend on the spin state of Co3＋ ions： in particular, the Eov of the HS states is lower than that of other spin states. This indicates that one can tune the properties of LaCoO3 by directly tuning the spin states of Co3＋ ions.展开更多
Metal-doped ceria catalysts have been applied in many important catalytic processes.In this work,we performed density functional theory calculations corrected by on-site Coulomb interactions to study the Pd-and Zr-dop...Metal-doped ceria catalysts have been applied in many important catalytic processes.In this work,we performed density functional theory calculations corrected by on-site Coulomb interactions to study the Pd-and Zr-doped CeO_(2)(111) surfaces with the dopant at different locations.The formation of oxygen vacancies and CO oxidation were systematically calculated on the various doped surfaces.We find that both Pd and Zr doping can activate the surface lattice O and reduce the energy barriers of CO oxidation.However,the promotion effect of the Zr dopant is limited to its existence in the first surface layer,while for the Pd dopant,the surface activity can be greatly enhanced even it occurs far below the surface.Besides,CO_(2) can be generated directly on the Pd-doped surfaces through reaction between CO and surface O,while the surface intermediate CO_(2)^(δ-) may readily form and restrict the releasing of CO_(2) by further oxidation to carbonates on the Zr-doped surfaces.Electronic analyses show that the doped Pd exists as Pd^(4+) and it has stronger electron affinity than other surface species during CO oxidation,contributing to the easy Pd^(4+) to Pd^(2+) transformation accompanied by direct CO_(2) formation at Pd-doped ceria.展开更多
The presence of chloride ions is the critical factor of passivity breakdown of the protective film and eventually leads to localized corrosion. However, the mechanism and the role of chlorides in these processes are s...The presence of chloride ions is the critical factor of passivity breakdown of the protective film and eventually leads to localized corrosion. However, the mechanism and the role of chlorides in these processes are still controversial. Hematite and chromia are generally believed to be the major components of outer and inner oxide layers on stainless steels. In the present paper, a comparative study of Cl ingress into pristine and defective α-Fe_(2)O_(3)(0001) surface, α-Cr_(2)O_(3)(0001) surface, along with their interface, was conducted using density functional theory. Vacancy formation energy calculation confirms good stability of α-Cr_(2)O_(3)and high reactive activity of the interface region. Cl inserts into an O vacancy is energetically more favorable than Fe vacancy and interstitial site, demonstrating Cl-induced degradation complies with the ion exchange model. Transition state search for Cl diffusion through O vacancies shows α-Cr_(2)O_(3)is more protective than α-Fe_(2)O_(3), while the interface region is the weak point of the duplex passive film.展开更多
The effects of Fe-C/N co-doping on the electronic and optical properties of NaTaO3 are studied with density func- tional theory. Our calculations indicate that mono-doped and co-doped sodium tantalate are both thermod...The effects of Fe-C/N co-doping on the electronic and optical properties of NaTaO3 are studied with density func- tional theory. Our calculations indicate that mono-doped and co-doped sodium tantalate are both thermodynamically stable. The co-doping sodium tantalate can reduce the energy band gap to a greater degree due to the synergistic effects of Fe and C （N） atoms than mono-doping sodium tantalate, and has a larger optical absorption of the whole visible spectrum. The band alignments for the doped NaTaO3 are well positioned for the feasibility of hydrogen production by water splitting. The Fe--C co-doping can enhance the absorption of the visible light and its photocatalytic activity more than Fe-N co-doping due to the different locations of impurity energy levels originating from their p-d hybridization effect.展开更多
Influence of doping and oxygen vacancy concentrations on oxygen ion or oxygen vacancy（V） migration energies of SmxCe1-xO2-δ（x = 0.0625, 0.125, 0.25 and δ = 0.0625, 0.125） systems using a GGA+U method are studied...Influence of doping and oxygen vacancy concentrations on oxygen ion or oxygen vacancy（V） migration energies of SmxCe1-xO2-δ（x = 0.0625, 0.125, 0.25 and δ = 0.0625, 0.125） systems using a GGA+U method are studied. Calculated results show that advantage migration types change from V?O2- to O2- ?V as x and δ increase. For V?O2- migrations of the Sm0.0625Ce0.9375O1.9375 and Sm0.125Ce0.875O1.9375 systems, electrostatic attractions between Sm3+ and V, defect associations between Ce3+ and V, and steric hindrances of Sm3+ affect the migration energies. For O2- ?V migrations of the Sm+（0.125）Ce0.875O1.875 and Sm0.25Ce0.75O1.875 systems, migration energies of O2- are affected by electrostatic repulsions between Sm3+ and O2- and defect associations between Ce3+ and V. Increases of the oxygen vacancy and Sm3+ doping concentrations benefit the oxygen ion and vacancy migrations, respectively.展开更多
An efficient and economical oxygen evolution reaction(OER)catalyst is critical to the widespread application of solar energy to fuel conversion.Among many potential OER catalysts,the metal oxyhydroxides,especially FeO...An efficient and economical oxygen evolution reaction(OER)catalyst is critical to the widespread application of solar energy to fuel conversion.Among many potential OER catalysts,the metal oxyhydroxides,especially FeOOH,show promising OER reactivity.In the present work,we performed a DFT+U study of the OER mechanism on theγ‐FeOOH(010)surface.In particular,we established the chemical potential of the OH?and hole pair and included the OH?anion in the reaction pathway,accounting to the alkaline conditions of anodic OER process.We then analyzed the OER pathways on the surface with OH‐,O‐and Fe‐terminations.On the surface with OH‐and O‐terminations,the O2molecule could form from either OH reacting with the surface oxygen species(-OH*and-O*)or the combination of two surface oxygen species.On the Fe‐terminated surface,O2can only form by adsorbing OH on the Fe sites first.The potential‐limiting step of the oxygen evolution with different surface terminations was determined by following the free‐energy change of the elementary steps along each pathway.Our results show that oxygen formation requires recreating the surface Fe sites,and consequently,the condition that favors the partially exposed Fe sites will promote oxygen formation.展开更多
First-principles calculations based on density functional theory corrected by Hubbard parameter U （DFT＋U） are applied to the study on the co-adsorption of O2 and H2O molecules to a-U（110） surface. The calculation...First-principles calculations based on density functional theory corrected by Hubbard parameter U （DFT＋U） are applied to the study on the co-adsorption of O2 and H2O molecules to a-U（110） surface. The calculation results show that DFT＋U method with Ueff = 1.5 eV can yield the experimental results of lattice constant and elastic modulus of a-uranium bulk well. Of all 7 low index surfaces of a-uranium, the （001） surface is the most stable with lowest surface energy while the （110） surface possesses the strongest activity with the highest surface energy. The adsorptions of O2 and H2O molecules are investigated separated. The O2 dissociates spontaneously in all initial configurations. For the adsorption of H2O molecule, both molecular and dissociative adsorptionsoccur. Through calculations of co-adsorption, it can be confirmed that the inhibition effect of O2 on the corrosion of uranium by water vapor originates from the preferential adsorption mechanism, while the consumption of H atoms by O atoms exerted little influence on the corrosion of uranium.展开更多
The density functional calculation is performed for centrosymmetric（La–Pm） GaO3 rare earth gallates, using a full potential linear augmented plane wave method with the LSDA and LSDA＋U exchange correlation to treat...The density functional calculation is performed for centrosymmetric（La–Pm） GaO3 rare earth gallates, using a full potential linear augmented plane wave method with the LSDA and LSDA＋U exchange correlation to treat highly correlated electrons due to the very localized 4f orbitals of rare earth elements, and explore the influence of U = 0.478 Ry on the magnetic phase stability and the densities of states. LSDA＋U calculation shows that the ferromagnetic（FM） state of RGaO3 is energetically more favorable than the anti-ferromagnetic（AFM） one, except for LaGaO3 where the NM state is the lowest in energy. The energy band gaps of RGaO3 are found to be in the range of 3.8–4.0 eV, indicating the semiconductor character with a large gap.展开更多
Hybrid density functional theory is employed to systematically investigate the structural,magnetic,vibrational,thermodynamic properties of plutonium monocarbide（Pu C and Pu C0.75）.For comparison,the results obtained...Hybrid density functional theory is employed to systematically investigate the structural,magnetic,vibrational,thermodynamic properties of plutonium monocarbide（Pu C and Pu C0.75）.For comparison,the results obtained by DFT,DFT ＋ U are also given.For Pu C and Pu C0.75,Fock-0.25 hybrid functional gives the best lattice constants and predicts the correct ground states of antiferromagnetic（AFM） structure.The calculated phonon spectra suggest that Pu C and Pu C0.75 are dynamically stable.Values of the Helmholtz free energy ？F,internal energy ？E,entropy S,and constant-volume specific heat Cv of Pu C and Pu C0.75 are given.The results are in good agreement with available experimental or theoretical data.As for the chemical bonding nature,the difference charge densities,the partial densities of states and the Bader charge analysis suggest that the Pu–C bonds of Pu C and Pu C0.75 have a mixture of covalent character and ionic character.The effect of carbon vacancy on the chemical bonding is also discussed in detail.We expect that our study can provide some useful reference for further experimental research on the phonon density of states,thermodynamic properties of the plutonium monocarbide.展开更多
Inspired by recent advancements in the field of single-atom magnets,particularly those involving rare-earth(RE)elements,we present a theoretical exploration employing DFT+U calculations to investigate the magnetic pro...Inspired by recent advancements in the field of single-atom magnets,particularly those involving rare-earth(RE)elements,we present a theoretical exploration employing DFT+U calculations to investigate the magnetic properties of selected 4f atoms,specifically Eu,Gd,and Ho,on a monolayer of the transition-metal dichalcogenide WSe_(2)in the 1H-phase.This study comparatively examines RE with diverse 4f orbital fillings and valence chemistry,aiming to understand how different coverage densities atop WSe_(2)affect magnetocrystalline anisotropy.We observe that RE lacking 5d occupation exhibit larger magnetic anisotropy energies at high densities,while those with outer 5d electrons show larger anisotropies in dilute configurations.Additionally,even half-filled 4f shell atoms with small orbital magnetic moments can generate substantial energy barriers for magnetization rotation due to prominent orbital hybridizations with WSe_(2).Open 4f shell atoms further enhance anisotropy barriers through spin-orbit coupling effects.These aspects are crucial for realizing stable magnetic information units experimentally.展开更多
While the accurate description of redox reactions remains a challenge for first-principles calculations,it has been shown that extended Hubbard functionals(DFT+U+V)can provide a reliable approach,mitigating self-inter...While the accurate description of redox reactions remains a challenge for first-principles calculations,it has been shown that extended Hubbard functionals(DFT+U+V)can provide a reliable approach,mitigating self-interaction errors,in materials with strongly localized d or f electrons.Here,we first show that DFT+U+V molecular dynamics is capable of following the adiabatic evolution of oxidation states over time,using representative Li-ion cathode materials.In turn,this allows to develop redoxaware machine-learning potentials.Weshowthat considering atoms with different oxidation states(as accurately predicted by DFT+U+V)as distinct species in the training leads to potentials that are able to identify the correct ground state and pattern of oxidation states for redox elements present.This can be achieved,e.g.,through a systematic combinatorial search for the lowest-energy configuration or with stochastic methods.This brings the advantages of machine-learning potentials to key technological applications(e.g.,rechargeable batteries),which require an accurate description of the evolution of redox states.展开更多
Weinvestigate the atomic and electronic structures of ferroelectric perovskite oxides,BaTiO_(3),PbTiO_(3),LiNbO_(3),and BiFeO_(3) using ab initio extended Hubbard functionals(DFT+U+V),where on-site and inter-site Hubb...Weinvestigate the atomic and electronic structures of ferroelectric perovskite oxides,BaTiO_(3),PbTiO_(3),LiNbO_(3),and BiFeO_(3) using ab initio extended Hubbard functionals(DFT+U+V),where on-site and inter-site Hubbard parameters are self-consistently determined via a pseudohybrid density functional by Agapito-Curtarolo-Buongiorno Nardelli.We compute band structures,ferroelectric distortions,polarization,Born effective charges,and switching barriers,compared with local density approximation,generalized gradient approximation(GGA),meta-GGA,and hybrid(HSE06)functionals.Results from DFT+U+V closely match experimental data,with the inter-site Hubbard terms significantly increasing band gaps,making closer alignment with GWresults.The crucial role of the inter-site Coulomb interactions,restoring polar distortions suppressed by on-site U is discussed.Our approach yields accuracy comparable to HSE06 at over an order-of-magnitude lower computational cost.This combination of accuracy and efficiency makes DFT+U+V well suited for high-throughput calculations and properties such as bulk photovoltaic effect and band alignments of ferroelectric heterostructures.展开更多
Density-functional theory with extended Hubbard functionals(DFT+U+V)provides a robust framework to accurately describe complex materials containing transition-metal or rare-earth elements.It does so by mitigating self...Density-functional theory with extended Hubbard functionals(DFT+U+V)provides a robust framework to accurately describe complex materials containing transition-metal or rare-earth elements.It does so by mitigating self-interaction errors inherent to semi-local functionals which are particularly pronounced in systems with partially-filled d and f electronic states.However,achieving accuracy in this approach hinges upon the accurate determination of the on-site U and inter-site V Hubbard parameters.In practice,these are obtained either by semi-empirical tuning,requiring prior knowledge,or,more correctly,by using predictive but expensive first-principles calculations.Here,we present a machine learning model based on equivariant neural networks which uses atomic occupation matrices as descriptors,directly capturing the electronic structure,local chemical environment,and oxidation states of the system at hand.We target here the prediction of Hubbard parameters computed self-consistently with iterative linear-response calculations,as implemented in density-functional perturbation theory(DFPT),and structural relaxations.Remarkably,when trained on data from 12 materials spanning various crystal structures and compositions,our model achieves mean absolute relative errors of 3%and 5%for Hubbard U and V parameters,respectively.By circumventing computationally expensive DFT or DFPT self-consistent protocols,our model significantly expedites the prediction of Hubbard parameters with negligible computational overhead,while approaching the accuracy of DFPT.Moreover,owing to its robust transferability,the model facilitates accelerated materials discovery and design via high-throughput calculations,with relevance for various technological applications.展开更多
The effects of cation ordering and surface compensating anions on the magnetic structure and catalytic properties of unilamellar Ni-Fe hydroxide nanosheets are studied by using the density functional theory （DFT） pl...The effects of cation ordering and surface compensating anions on the magnetic structure and catalytic properties of unilamellar Ni-Fe hydroxide nanosheets are studied by using the density functional theory （DFT） plus U method. Fe-segregation in the nanosheets yields magnetic domains with different spin alignments, while the surface compensating anions affect the local moments and valence states of the Fe atoms. The two conditions do not radically change the super-exchange nature of interactions between the paramagnetic metal centers, hut facilitate the formation of various magnetic superlattices in the nanosheets. The calculated free energy change of the intermediates shows that the most stable magnetic structure of Ni-Fe hydrox- ide nanosheets exhibits superior catalytic activity towards oxygen reduction/evolution reactions, which is indicative of magnetic catalyst. This is due to the cycle transition between Fe2＋ and Fe~~ ions in the reactions, which determines the sequence of cleavage of the O-H bond and the release of the OH group, controlling the rate-limiting steps of the reaction. The relationship of magnetism and catalytic activity of Ni-Fe hydroxide nanosheets is established by the valence state change of the Fe ions, which will be helpful to open the way for the design of hydroxide/layered double hydroxides （LDHs）-based magnetic catalysts.展开更多
基金This work was supported by the National Natural Science Foundation of China （No.U1232118, No.21203099）, the National Basic Research Program （No.2014CB932403）, the Program of Introducing Talents of Disciplines to China Universities （No.B06006）, Research Program for Advanced and Applied Technology of Tianjin （No.13JCYBJC36800）, Doctoral Fund of Ministry of Education of China （No.20120031120033）, Fok Ying Tung Education Foundation （No.151008）, and Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund （the second phase）. We appreciate the supports from the National Super-Computing Center at Tianjin and Guangzhou.
文摘By the first-principles calculations, most studies indicated that the （1102）-CoO2 termination of LaCoO3 cannot be stabilized, which disagrees with the experimental observation. Besides the crystal structure, we found that the spin states of Co3＋ ions could affect surface stability, which previously were not well considered. By examining the different states of Co3＋ ions in hexagonal-phase LaCoO3, including low spin, intermediate spin, and high spin states, the surface grand potentials of these facets are calculated and compared. The results show that the spin states of Co3＋ ions have an important influence on stability of the LaCoO3 facets. Different from the previous results, the stability diagrams demonstrate that the （1102）- CoO2 termination can stably exist under O-rich condition, which can get an agreement with the experimental ones. Furthermore, the surface oxygen vacancy formation energies （Eov） of stable facets are computed in different spin states. The Eov of these possible exposed terminations strongly depend on the spin state of Co3＋ ions： in particular, the Eov of the HS states is lower than that of other spin states. This indicates that one can tune the properties of LaCoO3 by directly tuning the spin states of Co3＋ ions.
基金Project supported by National Key R&D Program of China(2018YFA0208602)National Natural Science Foundation of China (21825301,22003016,92045303)+2 种基金the Fundamental Research Funds for the Central Universities(222201717003)Shanghai Municipal Science and Technology Major Project(2018SHZDZX03)the Programme of Introducing Talents of Discipline to Universities (B16017)。
文摘Metal-doped ceria catalysts have been applied in many important catalytic processes.In this work,we performed density functional theory calculations corrected by on-site Coulomb interactions to study the Pd-and Zr-doped CeO_(2)(111) surfaces with the dopant at different locations.The formation of oxygen vacancies and CO oxidation were systematically calculated on the various doped surfaces.We find that both Pd and Zr doping can activate the surface lattice O and reduce the energy barriers of CO oxidation.However,the promotion effect of the Zr dopant is limited to its existence in the first surface layer,while for the Pd dopant,the surface activity can be greatly enhanced even it occurs far below the surface.Besides,CO_(2) can be generated directly on the Pd-doped surfaces through reaction between CO and surface O,while the surface intermediate CO_(2)^(δ-) may readily form and restrict the releasing of CO_(2) by further oxidation to carbonates on the Zr-doped surfaces.Electronic analyses show that the doped Pd exists as Pd^(4+) and it has stronger electron affinity than other surface species during CO oxidation,contributing to the easy Pd^(4+) to Pd^(2+) transformation accompanied by direct CO_(2) formation at Pd-doped ceria.
基金supported by the Key Research Program of Frontier Sciences,CAS(No.QYZDY-SSW-JSC012)the Aeronautical Science Foundation of China(No.20200038092002)。
文摘The presence of chloride ions is the critical factor of passivity breakdown of the protective film and eventually leads to localized corrosion. However, the mechanism and the role of chlorides in these processes are still controversial. Hematite and chromia are generally believed to be the major components of outer and inner oxide layers on stainless steels. In the present paper, a comparative study of Cl ingress into pristine and defective α-Fe_(2)O_(3)(0001) surface, α-Cr_(2)O_(3)(0001) surface, along with their interface, was conducted using density functional theory. Vacancy formation energy calculation confirms good stability of α-Cr_(2)O_(3)and high reactive activity of the interface region. Cl inserts into an O vacancy is energetically more favorable than Fe vacancy and interstitial site, demonstrating Cl-induced degradation complies with the ion exchange model. Transition state search for Cl diffusion through O vacancies shows α-Cr_(2)O_(3)is more protective than α-Fe_(2)O_(3), while the interface region is the weak point of the duplex passive film.
基金supported by the National Natural Science Foundation of China(Grant Nos.51572219 and 11204239)the Project of the Natural Science Foundation of Shaanxi Province,China(Grant Nos.2015JM1018,2013JQ1018,and 15JK1714)+1 种基金the Project of Natural Science Foundation of Department of Education of Shaanxi Province,China(Grant No.15JK1759)the Science Foundation of Northwest University of China(Grant No.12NW06)
文摘The effects of Fe-C/N co-doping on the electronic and optical properties of NaTaO3 are studied with density func- tional theory. Our calculations indicate that mono-doped and co-doped sodium tantalate are both thermodynamically stable. The co-doping sodium tantalate can reduce the energy band gap to a greater degree due to the synergistic effects of Fe and C （N） atoms than mono-doping sodium tantalate, and has a larger optical absorption of the whole visible spectrum. The band alignments for the doped NaTaO3 are well positioned for the feasibility of hydrogen production by water splitting. The Fe--C co-doping can enhance the absorption of the visible light and its photocatalytic activity more than Fe-N co-doping due to the different locations of impurity energy levels originating from their p-d hybridization effect.
基金Supported by the National Natural Science Foundation of China(No.51474133)Inner Mongolia Natural Science Foundation(No.2016MS0513)
文摘Influence of doping and oxygen vacancy concentrations on oxygen ion or oxygen vacancy（V） migration energies of SmxCe1-xO2-δ（x = 0.0625, 0.125, 0.25 and δ = 0.0625, 0.125） systems using a GGA+U method are studied. Calculated results show that advantage migration types change from V?O2- to O2- ?V as x and δ increase. For V?O2- migrations of the Sm0.0625Ce0.9375O1.9375 and Sm0.125Ce0.875O1.9375 systems, electrostatic attractions between Sm3+ and V, defect associations between Ce3+ and V, and steric hindrances of Sm3+ affect the migration energies. For O2- ?V migrations of the Sm+（0.125）Ce0.875O1.875 and Sm0.25Ce0.75O1.875 systems, migration energies of O2- are affected by electrostatic repulsions between Sm3+ and O2- and defect associations between Ce3+ and V. Increases of the oxygen vacancy and Sm3+ doping concentrations benefit the oxygen ion and vacancy migrations, respectively.
基金supported by the Chemical,Biological,Environmental,and Transport Systems(CBET)program of US National Science Foundation(CBET-1438440)~~
文摘An efficient and economical oxygen evolution reaction(OER)catalyst is critical to the widespread application of solar energy to fuel conversion.Among many potential OER catalysts,the metal oxyhydroxides,especially FeOOH,show promising OER reactivity.In the present work,we performed a DFT+U study of the OER mechanism on theγ‐FeOOH(010)surface.In particular,we established the chemical potential of the OH?and hole pair and included the OH?anion in the reaction pathway,accounting to the alkaline conditions of anodic OER process.We then analyzed the OER pathways on the surface with OH‐,O‐and Fe‐terminations.On the surface with OH‐and O‐terminations,the O2molecule could form from either OH reacting with the surface oxygen species(-OH*and-O*)or the combination of two surface oxygen species.On the Fe‐terminated surface,O2can only form by adsorbing OH on the Fe sites first.The potential‐limiting step of the oxygen evolution with different surface terminations was determined by following the free‐energy change of the elementary steps along each pathway.Our results show that oxygen formation requires recreating the surface Fe sites,and consequently,the condition that favors the partially exposed Fe sites will promote oxygen formation.
基金Project supported by the National Nature Science Foundation of China(Grant Nos.51401237,11474358,and 51271198)
文摘First-principles calculations based on density functional theory corrected by Hubbard parameter U （DFT＋U） are applied to the study on the co-adsorption of O2 and H2O molecules to a-U（110） surface. The calculation results show that DFT＋U method with Ueff = 1.5 eV can yield the experimental results of lattice constant and elastic modulus of a-uranium bulk well. Of all 7 low index surfaces of a-uranium, the （001） surface is the most stable with lowest surface energy while the （110） surface possesses the strongest activity with the highest surface energy. The adsorptions of O2 and H2O molecules are investigated separated. The O2 dissociates spontaneously in all initial configurations. For the adsorption of H2O molecule, both molecular and dissociative adsorptionsoccur. Through calculations of co-adsorption, it can be confirmed that the inhibition effect of O2 on the corrosion of uranium by water vapor originates from the preferential adsorption mechanism, while the consumption of H atoms by O atoms exerted little influence on the corrosion of uranium.
文摘The density functional calculation is performed for centrosymmetric（La–Pm） GaO3 rare earth gallates, using a full potential linear augmented plane wave method with the LSDA and LSDA＋U exchange correlation to treat highly correlated electrons due to the very localized 4f orbitals of rare earth elements, and explore the influence of U = 0.478 Ry on the magnetic phase stability and the densities of states. LSDA＋U calculation shows that the ferromagnetic（FM） state of RGaO3 is energetically more favorable than the anti-ferromagnetic（AFM） one, except for LaGaO3 where the NM state is the lowest in energy. The energy band gaps of RGaO3 are found to be in the range of 3.8–4.0 eV, indicating the semiconductor character with a large gap.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21371160 and 21401173)
文摘Hybrid density functional theory is employed to systematically investigate the structural,magnetic,vibrational,thermodynamic properties of plutonium monocarbide（Pu C and Pu C0.75）.For comparison,the results obtained by DFT,DFT ＋ U are also given.For Pu C and Pu C0.75,Fock-0.25 hybrid functional gives the best lattice constants and predicts the correct ground states of antiferromagnetic（AFM） structure.The calculated phonon spectra suggest that Pu C and Pu C0.75 are dynamically stable.Values of the Helmholtz free energy ？F,internal energy ？E,entropy S,and constant-volume specific heat Cv of Pu C and Pu C0.75 are given.The results are in good agreement with available experimental or theoretical data.As for the chemical bonding nature,the difference charge densities,the partial densities of states and the Bader charge analysis suggest that the Pu–C bonds of Pu C and Pu C0.75 have a mixture of covalent character and ionic character.The effect of carbon vacancy on the chemical bonding is also discussed in detail.We expect that our study can provide some useful reference for further experimental research on the phonon density of states,thermodynamic properties of the plutonium monocarbide.
基金funded by the Deutsche Forschungsgemeinschaft(DFG)through CRC 1238,Control and Dynamics of Quantum Materials:Spin orbit coupling,correlations,and topology(Project No.277146847 C01)computing resources granted by RWTH Aachen University under Project No.jara0219.
文摘Inspired by recent advancements in the field of single-atom magnets,particularly those involving rare-earth(RE)elements,we present a theoretical exploration employing DFT+U calculations to investigate the magnetic properties of selected 4f atoms,specifically Eu,Gd,and Ho,on a monolayer of the transition-metal dichalcogenide WSe_(2)in the 1H-phase.This study comparatively examines RE with diverse 4f orbital fillings and valence chemistry,aiming to understand how different coverage densities atop WSe_(2)affect magnetocrystalline anisotropy.We observe that RE lacking 5d occupation exhibit larger magnetic anisotropy energies at high densities,while those with outer 5d electrons show larger anisotropies in dilute configurations.Additionally,even half-filled 4f shell atoms with small orbital magnetic moments can generate substantial energy barriers for magnetization rotation due to prominent orbital hybridizations with WSe_(2).Open 4f shell atoms further enhance anisotropy barriers through spin-orbit coupling effects.These aspects are crucial for realizing stable magnetic information units experimentally.
基金support by the European Commission through the MaX Centre of Excellence for supercomputing applications(grant number 101093374)We gratefully acknowledge support from the Deutsche Forschungsgemeinschaft(DFG)under Germany’s Excellence Strategy(EXC 2077,No.390741603,University Allowance,University of Bremen)Lucio Colombi Ciacchi,the host of the“U Bremen Excellence Chair Program.”We acknowledge support by the NCCR MARVEL,a National Centre of Competence in Research,funded by the Swiss National Science Foundation(grant number 205602).
文摘While the accurate description of redox reactions remains a challenge for first-principles calculations,it has been shown that extended Hubbard functionals(DFT+U+V)can provide a reliable approach,mitigating self-interaction errors,in materials with strongly localized d or f electrons.Here,we first show that DFT+U+V molecular dynamics is capable of following the adiabatic evolution of oxidation states over time,using representative Li-ion cathode materials.In turn,this allows to develop redoxaware machine-learning potentials.Weshowthat considering atoms with different oxidation states(as accurately predicted by DFT+U+V)as distinct species in the training leads to potentials that are able to identify the correct ground state and pattern of oxidation states for redox elements present.This can be achieved,e.g.,through a systematic combinatorial search for the lowest-energy configuration or with stochastic methods.This brings the advantages of machine-learning potentials to key technological applications(e.g.,rechargeable batteries),which require an accurate description of the evolution of redox states.
基金supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (No. RS-2024-00358551)by the Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education (No. RS-2021-NR060129)+2 种基金S.Y.P. and M.C.C. were supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education (No. RS-2021-NR060140)Y.-W.S. was supported by KIAS individual Grant (No. CG031509)W.Y. was supported by KIAS individual Grant (No. QP090102). Computations were also supported by the CAC of KIAS.
文摘Weinvestigate the atomic and electronic structures of ferroelectric perovskite oxides,BaTiO_(3),PbTiO_(3),LiNbO_(3),and BiFeO_(3) using ab initio extended Hubbard functionals(DFT+U+V),where on-site and inter-site Hubbard parameters are self-consistently determined via a pseudohybrid density functional by Agapito-Curtarolo-Buongiorno Nardelli.We compute band structures,ferroelectric distortions,polarization,Born effective charges,and switching barriers,compared with local density approximation,generalized gradient approximation(GGA),meta-GGA,and hybrid(HSE06)functionals.Results from DFT+U+V closely match experimental data,with the inter-site Hubbard terms significantly increasing band gaps,making closer alignment with GWresults.The crucial role of the inter-site Coulomb interactions,restoring polar distortions suppressed by on-site U is discussed.Our approach yields accuracy comparable to HSE06 at over an order-of-magnitude lower computational cost.This combination of accuracy and efficiency makes DFT+U+V well suited for high-throughput calculations and properties such as bulk photovoltaic effect and band alignments of ferroelectric heterostructures.
基金support by the NCCR MARVEL,a National Centre of Competence in Research,funded by the Swiss National Science Foundation(Grant number 205602)supported by a grant from the Swiss National Supercomputing Centre(CSCS)under project ID s1073(Piz Daint)and ID 465000416(LUMI-G)supported by MIAI@Grenoble Alpes,(ANR-19-P3IA-0003).
文摘Density-functional theory with extended Hubbard functionals(DFT+U+V)provides a robust framework to accurately describe complex materials containing transition-metal or rare-earth elements.It does so by mitigating self-interaction errors inherent to semi-local functionals which are particularly pronounced in systems with partially-filled d and f electronic states.However,achieving accuracy in this approach hinges upon the accurate determination of the on-site U and inter-site V Hubbard parameters.In practice,these are obtained either by semi-empirical tuning,requiring prior knowledge,or,more correctly,by using predictive but expensive first-principles calculations.Here,we present a machine learning model based on equivariant neural networks which uses atomic occupation matrices as descriptors,directly capturing the electronic structure,local chemical environment,and oxidation states of the system at hand.We target here the prediction of Hubbard parameters computed self-consistently with iterative linear-response calculations,as implemented in density-functional perturbation theory(DFPT),and structural relaxations.Remarkably,when trained on data from 12 materials spanning various crystal structures and compositions,our model achieves mean absolute relative errors of 3%and 5%for Hubbard U and V parameters,respectively.By circumventing computationally expensive DFT or DFPT self-consistent protocols,our model significantly expedites the prediction of Hubbard parameters with negligible computational overhead,while approaching the accuracy of DFPT.Moreover,owing to its robust transferability,the model facilitates accelerated materials discovery and design via high-throughput calculations,with relevance for various technological applications.
基金supported by the National Natural Science Foundation of China (21431003)the National Program on Key Basic Research Project (2014CB932101)the Fundamental Research Funds for the Central Universities (buctrc201514)
文摘The effects of cation ordering and surface compensating anions on the magnetic structure and catalytic properties of unilamellar Ni-Fe hydroxide nanosheets are studied by using the density functional theory （DFT） plus U method. Fe-segregation in the nanosheets yields magnetic domains with different spin alignments, while the surface compensating anions affect the local moments and valence states of the Fe atoms. The two conditions do not radically change the super-exchange nature of interactions between the paramagnetic metal centers, hut facilitate the formation of various magnetic superlattices in the nanosheets. The calculated free energy change of the intermediates shows that the most stable magnetic structure of Ni-Fe hydrox- ide nanosheets exhibits superior catalytic activity towards oxygen reduction/evolution reactions, which is indicative of magnetic catalyst. This is due to the cycle transition between Fe2＋ and Fe~~ ions in the reactions, which determines the sequence of cleavage of the O-H bond and the release of the OH group, controlling the rate-limiting steps of the reaction. The relationship of magnetism and catalytic activity of Ni-Fe hydroxide nanosheets is established by the valence state change of the Fe ions, which will be helpful to open the way for the design of hydroxide/layered double hydroxides （LDHs）-based magnetic catalysts.
