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Chris Wolverton - One of the best experts on this subject based on the ideXlab platform.
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performance of the strongly constrained and appropriately normed density functional for solid state materials
Physical Review Materials, 2018Co-Authors: Eric B Isaacs, Chris WolvertonAbstract:Constructed to satisfy 17 known exact constraints for a semilocal density functional, the strongly constrained and appropriately normed (SCAN) meta-generalized-gradient-approximation functional has shown early promise for accurately describing the electronic structure of molecules and solids. One open question is how well SCAN predicts the Formation Energy, a key quantity for describing the thermodynamic stability of solid-state compounds. To answer this question, we perform an extensive benchmark of SCAN by computing the Formation energies for a diverse group of nearly 1000 crystalline compounds for which experimental values are known. Due to an enhanced exchange interaction in the covalent bonding regime, SCAN substantially decreases the Formation Energy errors for strongly bound compounds, by approximately 50% to 110 meV/atom, as compared to the generalized gradient approximation of Perdew, Burke, and Ernzerhof (PBE). However, for intermetallic compounds, SCAN performs moderately worse than PBE with an increase in Formation Energy error of approximately 20%, stemming from SCAN's distinct behavior in the weak bonding regime. The Formation Energy errors can be further reduced via elemental chemical potential fitting. We find that SCAN leads to significantly more accurate predicted crystal volumes, moderately enhanced magnetism, and mildly improved band gaps as compared to PBE. Overall, SCAN represents a significant improvement in accurately describing the thermodynamics of strongly bound compounds.
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Performance of the strongly constrained and appropriately normed density functional for solid-state materials
Physical Review Materials, 2018Co-Authors: Eric B Isaacs, Chris WolvertonAbstract:Constructed to satisfy all known exact constraints and appropriate norms for a semilocal density functional, the strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation functional has shown early promise for accurately describing the electronic structure of molecules and solids. One open question is how well SCAN predicts the Formation Energy, a key quantity for describing the thermodynamic stability of solid-state compounds. To answer this question, we perform an extensive benchmark of SCAN by computing the Formation energies for a diverse group of nearly one thousand crystalline compounds for which experimental values are known. Due to an enhanced exchange interaction in the covalent bonding regime, SCAN substantially decreases the Formation Energy errors for strongly-bound compounds, by approximately 50% to 110 meV/atom, as compared to the generalized gradient approximation of Perdew, Burke, and Ernzerhof (PBE). However, for intermetallic compounds, SCAN performs moderately worse than PBE with an increase in Formation Energy error of approximately 20%, stemming from SCAN's distinct behavior in the weak bonding regime. The Formation Energy errors can be further reduced via elemental chemical potential fitting. We find that SCAN leads to significantly more accurate predicted crystal volumes, moderately enhanced magnetism, and mildly improved band gaps as compared to PBE. Overall, SCAN represents a significant improvement in accurately describing the thermodynamics of strongly-bound compounds.
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high throughput dft calculations of Formation Energy stability and oxygen vacancy Formation Energy of abo 3 perovskites
Scientific Data, 2017Co-Authors: Antoine Emery, Chris WolvertonAbstract:ABO3 perovskites are oxide materials that are used for a variety of applications such as solid oxide fuel cells, piezo-, ferro-electricity and water splitting. Due to their remarkable stability with respect to cation substitution, new compounds for such applications potentially await discovery. In this work, we present an exhaustive dataset of Formation energies of 5,329 cubic and distorted perovskites that were calculated using first-principles density functional theory. In addition to Formation energies, several additional properties such as oxidation states, band gap, oxygen vacancy Formation Energy, and thermodynamic stability with respect to all phases in the Open Quantum Materials Database are also made publicly available. This large dataset for this ubiquitous crystal structure type contains 395 perovskites that are predicted to be thermodynamically stable, of which many have not yet been experimentally reported, and therefore represent theoretical predictions. The dataset thus opens avenues for future use, including materials discovery in many research-active areas.
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high throughput computational screening of perovskites for thermochemical water splitting applications
Chemistry of Materials, 2016Co-Authors: Antoine Emery, Vinay Hegde, James E Saal, Scott Kirklin, Chris WolvertonAbstract:The use of hydrogen as fuel is a promising avenue to aid in the reduction of greenhouse effect gases released in the atmosphere. In this work, we present a high-throughput density functional theory (HT-DFT) study of 5,329 cubic and distorted perovskite ABO3 compounds to screen for thermodynamically favorable two-step thermochemical water splitting (TWS) materials. From a data set of more than 11,000 calculations, we screened materials based on the following: (a) thermodynamic stability and (b) oxygen vacancy Formation Energy that allow favorable TWS. From our screening strategy, we identify 139 materials as potential new candidates for TWS application. Several of these compounds, such as CeCoO3 and BiVO3, have not been experimentally explored yet for TWS and present promising avenues for further research. We show that taking into consideration all phases present in the A–B–O ternary phase, as opposed to only calculating the Formation Energy of a compound, is crucial to assess correctly the stability of a ...
M H N Assadi - One of the best experts on this subject based on the ideXlab platform.
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selecting the suitable dopants electronic structures of transition metal and rare earth doped thermoelectric sodium cobaltate
RSC Advances, 2013Co-Authors: M H N AssadiAbstract:Engineered Na0.75CoO2 is considered a prime candidate to achieve high efficiency thermoelectric systems to regenerate electricity from waste heat. In this work, three elements with outmost electronic configurations, (1) an open d shell (Ni), (2) a closed d shell (Zn), and (3) a half filled f shell (Eu) with maximum unpaired electrons, were selected to outline the dopants' effects on the electronic and crystallographic structures of Na0.75CoO2. Systematic ab initio density functional calculations with DMOL3 package showed that the Ni and Zn were more stable when substituting Co with Formation Energy −2.35 eV, 2.08 eV when Fermi level equals the valence band maximum. While Eu is more stable when it substitutes Na having a Formation Energy of −2.64 eV. As these results show great harmony with existing experimental data, they provide new insights into the fundamental principle of dopant selection for manipulating the physical properties in the development of high performance sodium cobaltate based multifunctional materials.
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selecting the suitable dopants electronic structures of transition metal and rare earth doped thermoelectric sodium cobaltate
arXiv: Chemical Physics, 2012Co-Authors: M H N AssadiAbstract:Engineered $Na_{0.75}CoO_2$ is considered a prime candidate to achieve high-efficiency thermoelectric systems to regenerate electricity from waste heat. In this work, three elements with outmost electronic configurations, (1) an open d shell (Ni), (2) a closed d shell (Zn), and (3) a half filled f shell (Eu) with maximum unpaired electrons, were selected to outline the dopants' effects on electronic and crystallographic structures of $Na_{0.75}CoO_2$. Systematic $ab$ $initio$ density functional calculations with $DMOL^3$ package showed that the Ni and Zn were more stable when substituting Co with Formation Energy $-2.35$ eV, $2.08$ eV when Fermi level equals to the valence band maximum. While Eu is more stable when it substitutes Na having Formation Energy of $-2.64$ eV. As these results show great harmony with existing experimental data, they provide new insights into the fundamental principle of dopant selection for manipulating the physical properties in the development of high-performance sodium cobaltate based multifunctional materials.
J. Robertson - One of the best experts on this subject based on the ideXlab platform.
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band structure band offsets and intrinsic defect properties of few layer arsenic and antimony
The Journal of Physical Chemistry, 2020Co-Authors: Ting Wang, J. RobertsonAbstract:We present a detailed first-principle study of few-layer arsenic and antimony electronic structures. The band structures of 2D arsenic and antimony are calculated by a hybrid functional with the spin–orbital coupling. The results show that the band gaps of arsenene (monolayer arsenic) and antimonene (monolayer antimony) are 1.93 and 1.52 eV, respectively. It is observed that the band gaps narrow in trilayer arsenic and bilayer antimony. The band alignment with HfO₂ and other 2D materials is calculated to show that HfO₂ is a good candidate as a gate oxide in field effect transistors. It is found that point defects such as a single vacancy or adatom will introduce several defect states in arsenene in the middle of the band gap. Meanwhile, the defect Formation Energy becomes negative when the Fermi level is close to the band edges. By comparison, the defect Formation Energy in antimonene is always positive so that the Fermi level pinning should be suppressed in contact with the reactive metal.
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impact of oxygen exchange reaction at the ohmic interface in ta2o5 based reram devices
Nanoscale, 2016Co-Authors: Stephan Menzel, J. Robertson, D J Wouters, Bernd Roesgen, Rainer Waser, Vikas RanaAbstract:Interface reactions constitute essential aspects of the switching mechanism in redox-based resistive random access memory (ReRAM). For example, the modulation of the electronic barrier height at the Schottky interface is considered to be responsible for the toggling of the resistance states. On the other hand, the role of the ohmic interface in the resistive switching behavior is still ambigious. In this paper, the impact of different ohmic metal-electrode (M) materials, namely W, Ta, Ti, and Hf on the characteristics of Ta2O5 ReRAM is investigated. These materials are chosen with respect to their free Energy for metal oxide Formation and, associated, their impact on the Formation Energy of oxygen vacancy defects at the M/Ta2O5 interface. The resistive switching devices with Ti and Hf electrodes that have a negative defect Formation Energy, show an early RESET failure during the switching cycles. This failure process with Ti and Hf electrode is attributed to the accumulation of oxygen vacancies in the Ta2O5 layer, which leads to permanent breakdown of the metal–oxide to a low resistive state. In contrast, the defect Formation Energy in the Ta2O5 with respect to Ta and W electrodes is positive and for those highly stable resistive switching behavior is observed. During the quasi-static and transient-pulse characterization, the ReRAM devices with the W electrode consistently show an increased high resistance state (HRS) than with the Ta electrode for all RESET stop voltages. This effect is attributed to the faster oxygen exchange reaction at the W-electrode interface during the RESET process in accordance to lower stability of WO3 than Ta2O5. Based on these findings, an advanced resistive switching model, wherein also the oxygen exchange reaction at the ohmic M-electrode interface plays a vital role in determining of the resistance states, is presented.
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Sulfur vacancies in monolayer MoS2 and its electrical contacts
Applied Physics Letters, 2013Co-Authors: D. Liu, L. Fang, Ying Guo, J. RobertsonAbstract:The use of reactive electropositive metal contacts is proposed to lower contact resistance in MoS 2 devices, based on calculations of the sulfur vacancy in MoS 2 by the screened exchange (sX) hybrid functional. sX gives band gaps of 1.88 eV and 1.34 eV for monolayer and bulk MoS 2 . The S vacancy has a Formation Energy of 2.35 eV in S-rich conditions, while the Mo vacancy has a large Formation Energy of 8.02 eV in Mo-rich conditions. The S vacancy introduces defect levels 0/-1 at 1.23 eV and -1/-2 at 1.28 eV in the upper gap. Its Formation Energy becomes small or negative for E F near the conduction band edge, leading to E F pinning near the conduction band for reactive metal contacts and lower contact resistances. © 2013 AIP Publishing LLC.
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defect energies of graphite density functional calculations
Physical Review B, 2005Co-Authors: Stephanie Reich, J. RobertsonAbstract:The energies of point defects in graphite have been calculated from first principles. The various interplane interstitial configurations are found to have a wider range of energies than in some earlier calculations, implying a larger interstitial migration Energy than previously expected $(g1.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$. Interplane interstitials are found to be stabilized by a shear of one graphite plane with respect to its neighbors, as this allows the interstitial to bond to three or four atoms in two planes in the ylid and spiro configurations. The minimum interstitial Formation Energy in sheared graphite is only $5.3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ compared to $6.3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ in perfect graphite. Such interstitials form a strongly bound vacancy-interstitial pair with a Formation Energy of only $10.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The Formation Energy of a single vacancy is $7.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The Formation Energy and the activation barrier of the Stone-Wales defect in a single layer of graphite were also calculated.
J J Terblans - One of the best experts on this subject based on the ideXlab platform.
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temperature and surface orientation dependent calculated vacancy Formation Energy for cu nanocubes
Journal of Materials Science, 2018Co-Authors: C Van Der Walt, J J Terblans, H C SwartAbstract:Cu nanocubes of different sizes were simulated using the Sutton–Chen molecular dynamics model. For each size, the rhombicuboctahedron shape that minimized the internal cohesive Energy of the particle was chosen. Each particle’s thermodynamic properties were investigated by calculating the average potential Energy per atom for each particle over temperature. The vacancy Formation Energy of the particles as well as the internal binding Energy and surface binding energies of each particle was also characterized. The nanocube melting temperatures, surface energies indicating reactivity, and cohesive Energy, indicating particle stability, were characterized and compared for different particle sizes and shapes.
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calculated bulk vacancy Formation Energy ev for a schottky defect in al single crystals
Surface and Interface Analysis, 2003Co-Authors: J J TerblansAbstract:In this paper the bulk vacancy Formation energies (Ev) of Al single crystals (with different surface orientations (111), (100) and (110)) were calculated with the embedded atom method using the empirical many-body potential of Sutton and Chen. These calculations indicate that there is a significant difference in the bulk vacancy Formation Energy underneath different surface orientations. The crystal with the (111) surface had the highest bulk vacancy Formation Energy and the crystal with the (110) surface had the lowest bulk vacancy Formation Energy. Copyright © 2003 John Wiley & Sons, Ltd.
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calculating the bulk vacancy Formation Energy ev for a schottky defect in a perfect cu 111 cu 100 and a cu 110 single crystal
Surface and Interface Analysis, 2002Co-Authors: J J TerblansAbstract:A study has been made of the bulk vacancy Formation Energy (E v ) of Cu by calculating the bulk vacancy Formation Energy for Cu single crystals with different surface orientations (E (111) v ∼1.54 eV, E (100) v ∼ 1.34 eV and E (100) v ∼ 1.07 eV). The calculations were performed with the empirical many-body potentials of Sutton and Chen. The calculations indicate a significant difference in the bulk vacancy Formation Energy under different surface orientations. The bulk vacancy Formation energies were also used to calculate theoretical bulk diffusion coefficients beneath the different surface orientations. These theoretical bulk diffusion coefficients were compared with experimental bulk diffusion coefficients that were calculated from kinetic bulk to surface segregation measurements of Sb that segregates to a Cu(111) and a Cu(110) surface. The calculated bulk diffusion coefficients and the experimental bulk diffusion coefficients showed the same trend regarding the different surface orientations.
Michael J Janik - One of the best experts on this subject based on the ideXlab platform.
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interaction trends between single metal atoms and oxide supports identified with density functional theory and statistical learning
Nature Catalysis, 2018Co-Authors: Nolan Oconnor, Michael J Janik, A S M Jonayat, Thomas P SenftleAbstract:Single-atom catalysts offer high reactivity and selectivity while maximizing utilization of the expensive active metal component. However, they are susceptible to sintering, where single metal atoms agglomerate into thermodynamically stable clusters. Tuning the binding strength between single metal atoms and oxide supports is essential to prevent sintering. We apply density functional theory, together with a statistical learning approach based on least absolute shrinkage and selection operator regression, to identify property descriptors that predict interaction strengths between single metal atoms and oxide supports. Here, we show that interfacial binding is correlated with readily available physical properties of both the supported metal, such as oxophilicity measured by oxide Formation Energy, and the support, such as reducibility measured by oxygen vacancy Formation Energy. These properties can be used to empirically screen interaction strengths between metal–support pairs, thus aiding the design of single-atom catalysts that are robust against sintering.
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correlation of methane activation and oxide catalyst reducibility and its implications for oxidative coupling
ACS Catalysis, 2016Co-Authors: Gaurav Kumar, Sai Lap Jacky Lau, Matthew D Krcha, Michael J JanikAbstract:We investigate methane activation over a range of metal-oxide surfaces. Density functional theory calculations are used to correlate the C–H bond activation Energy to the surface reducibility (oxygen vacancy Formation Energy, work function). The correlation includes several reducible and nonreducible metal-oxides, doped CeO2, doped TiO2, ZnO, and doped MgO, and also holds for various oxidation states of TbOx, different surface facets of TiO2, and variation of Hubbard U parameter for CeO2. We find a linear correlation between the C–H activation reaction Energy, ·CH3 adsorption Energy, and the oxygen vacancy Formation Energy of pure/doped metal-oxides, making surface reducibility a descriptor for predicting catalyst activity and selectivity against further oxidation of the ·CH3 radical.