The standard approach for predicting defect equilibria from first principles assumes that the solidstate system is initially in a thermodynamic equilibrium with the external atomic reservoirs.This“growth step”is the...The standard approach for predicting defect equilibria from first principles assumes that the solidstate system is initially in a thermodynamic equilibrium with the external atomic reservoirs.This“growth step”is then often followed by a temperature quench in a“pseudo-equilibrium”in which some or all defect concentrations are frozen in until only the Fermi level EF remains to be equilibrated.However,this protocol does not account for the possibility of site exchanges which can create important defect redistributions as long as short-range defect migration is kinetically permissible.To model this redistribution,we developed an approach to solve for the non-equilibrium chemical potentials as a function of temperature while maintaining the overall defect stoichiometry.We then apply this approach to the Dirac semimetal Cd_(3)As_(2) to model extrinsic doping with group 1/11 and 14 elements.Undoped Cd_(3)As_(2) exhibits an undesirable mismatch between EF and the Dirac point.This unintentional electron doping originates from intrinsic defects and is difficult to overcome through adjustment of synthesis conditions alone.Employing our pseudo-equilibrium modeling,we identify extrinsic doping strategies for realizing doping-balanced Cd_(3)As_(2) at the relatively low temperatures accessible in thin-film growth of this material.展开更多
The performance of density functional theory approximations for predicting materials thermodynamics is typically assessed by comparing calculated and experimentally determined enthalpies of formation from elemental ph...The performance of density functional theory approximations for predicting materials thermodynamics is typically assessed by comparing calculated and experimentally determined enthalpies of formation from elemental phases,ΔH_(f).However,a compound competes thermodynamically with both other compounds and their constituent elemental forms,and thus,the enthalpies of the decomposition reactions to these competing phases,ΔH_(d),determine thermodynamic stability.We evaluated the phase diagrams for 56,791 compounds to classify decomposition reactions into three types:1.those that produce elemental phases,2.those that produce compounds,and 3.those that produce both.This analysis shows that the decomposition into elemental forms is rarely the competing reaction that determines compound stability and that approximately two-thirds of decomposition reactions involve no elemental phases.Using experimentally reported formation enthalpies for 1012 solid compounds,we assess the accuracy of the generalized gradient approximation(GGA)(PBE)and meta-GGA(SCAN)density functionals for predicting compound stability.For 646 decomposition reactions that are not trivially the formation reaction,PBE(mean absolute difference between theory and experiment(MAD)=70 meV/atom)and SCAN(MAD=59 meV/atom)perform similarly,and commonly employed correction schemes using fitted elemental reference energies make only a negligible improvement(~2 meV/atom).Furthermore,for 231 reactions involving only compounds(Type 2),the agreement between SCAN,PBE,and experiment is within~35 meV/atom and is thus comparable to the magnitude of experimental uncertainty.展开更多
Entropic stabilized ABO_(3) perovskite oxides promise many applications,including the two-step solar thermochemical hydrogen(STCH)production.Using binary and quaternary A-site mixed{A}FeO_(3) as a model system,we reve...Entropic stabilized ABO_(3) perovskite oxides promise many applications,including the two-step solar thermochemical hydrogen(STCH)production.Using binary and quaternary A-site mixed{A}FeO_(3) as a model system,we reveal that as more cation types,especially above four,are mixed on the A-site,the cell lattice becomes more cubic-like but the local Fe–O octahedrons are more distorted.By comparing four different Density Functional Theory-informed statistical models with experiments,we show that the oxygen vacancy formation energies(E^(f)_(V))distribution and the vacancy interactions must be considered to predict the oxygen non-stoichiometry(δ)accurately.For STCH applications,the E^(f)_(V) distribution,including both the average and the spread,can be optimized jointly to improveΔδ(difference ofδbetween the two-step conditions)in some hydrogen production levels.This model can be used to predict the range of water splitting that can be thermodynamically improved by mixing cations in{A}FeO_(3) perovskites.展开更多
We present a new solid-state material phase which is a disordered solid solution but offers many ordered line-compound features.The emergent physical phenomena are rooted in the perfect short-range order which conserv...We present a new solid-state material phase which is a disordered solid solution but offers many ordered line-compound features.The emergent physical phenomena are rooted in the perfect short-range order which conserves the local octet rule.We model the dual-sublattice-mixed semiconductor alloy (ZnSnN_(2))_(1-x)(ZnO)_(2x) using first-principles calculations,Monte-Carlo simulations with a model Hamiltonian,and an extension of the regular solution model by incorporating short-range order.展开更多
基金supported as part of the project “Disorder in Topological Semimetals”, funded by the U.S. Departmentof Energy (DOE), Office of Science (SC), Basic Energy Sciences, Physical Behavior of Materials programThe National Renewable Energy Laboratory (NREL) is operated under Contract No. DE-AC36-08GO28308The research used High-Performance Computing (HPC) resources of the National Energy Research Scientific Computing Center (NERSC), a DOE-SC user facility located at Lawrence Berkeley National Laboratory, operated under Contract No. DEAC02-05CH11231. This research also used HPC resources at NREL, sponsored by DOE, Office of Energy Efficiency and Renewable Energy. The views expressed in the article do not necessarily represent the views of DOE or the U.S. Government.
文摘The standard approach for predicting defect equilibria from first principles assumes that the solidstate system is initially in a thermodynamic equilibrium with the external atomic reservoirs.This“growth step”is then often followed by a temperature quench in a“pseudo-equilibrium”in which some or all defect concentrations are frozen in until only the Fermi level EF remains to be equilibrated.However,this protocol does not account for the possibility of site exchanges which can create important defect redistributions as long as short-range defect migration is kinetically permissible.To model this redistribution,we developed an approach to solve for the non-equilibrium chemical potentials as a function of temperature while maintaining the overall defect stoichiometry.We then apply this approach to the Dirac semimetal Cd_(3)As_(2) to model extrinsic doping with group 1/11 and 14 elements.Undoped Cd_(3)As_(2) exhibits an undesirable mismatch between EF and the Dirac point.This unintentional electron doping originates from intrinsic defects and is difficult to overcome through adjustment of synthesis conditions alone.Employing our pseudo-equilibrium modeling,we identify extrinsic doping strategies for realizing doping-balanced Cd_(3)As_(2) at the relatively low temperatures accessible in thin-film growth of this material.
基金This work was supported by the National Science Foundation(award nos.CBET-1433521,CHE-1800592,and CBET-1806079)The authors also acknowledge partial support for this work from the U.S.Department of Energy,Office of Basic Energy Sciences(S.L.and A.M.H.,contract no.DE-AC36-08GO28308)Fuel Cell Technologies Office(A.W.W.and C.B.M,award no.DE-EE0008088).
文摘The performance of density functional theory approximations for predicting materials thermodynamics is typically assessed by comparing calculated and experimentally determined enthalpies of formation from elemental phases,ΔH_(f).However,a compound competes thermodynamically with both other compounds and their constituent elemental forms,and thus,the enthalpies of the decomposition reactions to these competing phases,ΔH_(d),determine thermodynamic stability.We evaluated the phase diagrams for 56,791 compounds to classify decomposition reactions into three types:1.those that produce elemental phases,2.those that produce compounds,and 3.those that produce both.This analysis shows that the decomposition into elemental forms is rarely the competing reaction that determines compound stability and that approximately two-thirds of decomposition reactions involve no elemental phases.Using experimentally reported formation enthalpies for 1012 solid compounds,we assess the accuracy of the generalized gradient approximation(GGA)(PBE)and meta-GGA(SCAN)density functionals for predicting compound stability.For 646 decomposition reactions that are not trivially the formation reaction,PBE(mean absolute difference between theory and experiment(MAD)=70 meV/atom)and SCAN(MAD=59 meV/atom)perform similarly,and commonly employed correction schemes using fitted elemental reference energies make only a negligible improvement(~2 meV/atom).Furthermore,for 231 reactions involving only compounds(Type 2),the agreement between SCAN,PBE,and experiment is within~35 meV/atom and is thus comparable to the magnitude of experimental uncertainty.
基金This work is supported by the U.S.Department of Energy’s Office of Energy Efficiency and Renewable Energy(EERE)under Agreement Number DE-EE0008839managed by the Hydrogen and Fuel Cell Technologies Office in the Fiscal Year 2019 H2@SCALE program+1 种基金The Alliance for Sustainable Energy,LLC,operates and manages the National Renewable Energy Laboratory for the US.Department of Energy(DOE)under Contract No.DE-AC36-08GO28308The research was performed using computational resources sponsored by the Department of Energy’s Office of Energy Efficiency and Renewable Energy and located at the National Renewable Energy Laboratory and was conducted using computational resources and services at the Center for Computation and Visualization,Brown University.
文摘Entropic stabilized ABO_(3) perovskite oxides promise many applications,including the two-step solar thermochemical hydrogen(STCH)production.Using binary and quaternary A-site mixed{A}FeO_(3) as a model system,we reveal that as more cation types,especially above four,are mixed on the A-site,the cell lattice becomes more cubic-like but the local Fe–O octahedrons are more distorted.By comparing four different Density Functional Theory-informed statistical models with experiments,we show that the oxygen vacancy formation energies(E^(f)_(V))distribution and the vacancy interactions must be considered to predict the oxygen non-stoichiometry(δ)accurately.For STCH applications,the E^(f)_(V) distribution,including both the average and the spread,can be optimized jointly to improveΔδ(difference ofδbetween the two-step conditions)in some hydrogen production levels.This model can be used to predict the range of water splitting that can be thermodynamically improved by mixing cations in{A}FeO_(3) perovskites.
基金This work was supported by the U.S.Department of Energy(DOE)under Contract No.DE-AC36-08GO28308 with the Alliance for Sustainable Energy,LLC,the manager and operator of the National Renewable Energy Laboratory.
文摘We present a new solid-state material phase which is a disordered solid solution but offers many ordered line-compound features.The emergent physical phenomena are rooted in the perfect short-range order which conserves the local octet rule.We model the dual-sublattice-mixed semiconductor alloy (ZnSnN_(2))_(1-x)(ZnO)_(2x) using first-principles calculations,Monte-Carlo simulations with a model Hamiltonian,and an extension of the regular solution model by incorporating short-range order.
