Publisher's Note: Density functional theory study of clean, hydrated, and defective alumina<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mn>1</mml:mn><mml:mover accent="true"><mml:mn>1</mml:mn><mml:mo stretchy="false">¯</mml:mo></mml:mover><mml:mn>02</mml:mn></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math>surfaces [Phys. Rev. B<b>81</b>, 125423 (2010)]

Mason, Sara E.; Iceman, Christopher; Trainor, Thomas P.; Chaka, Anne M.

doi:10.1103/physrevb.81.169901

Cited by 14 publications

(18 citation statements)

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“…51 As is common practice in ab initio thermodynamics, 26,35,47,49 the energy of the O 2 molecule was corrected with the experimental atomization energy because of the large error (0.90 eV) in the GGA atomization energy. The heat of formation of β-MnO 2 at 0 K (left-hand side of eq 9 in parentheses) is therefore calculated to be −5.88 eV, giving a lower limit of −2.94 eV for μ O .…”

Section: ■ Methodsmentioning

confidence: 99%

Structure and Stability of Hydrated β-MnO₂ Surfaces

Oxford

Chaka

2012

J. Phys. Chem. C

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Hydration of the β-MnO 2 (110), (100), and (101) surfaces is investigated using a combination of periodic density functional theory and ab initio thermodynamics. Fully hydrated surfaces are found to be significantly more stable than the stoichiometric ones up to temperatures in the range of 650 to 730 K at ambient oxygen and water partial pressures. A mixture of molecular and dissociative water adsorption is predicted to occur on the (110) and (101) surfaces, while the (100) surface does not dissociate water. Changes in surface reactivity upon water adsorption are explored via partial density of states analysis. Differences in surface relaxations and vibrational spectra are discussed and can be used to identify the type of adsorption mode. ■ INTRODUCTIONManganese oxides are commonly found throughout the environment and have been recognized for their technological significance for centuries. 1 In recent times, the advantages of using manganese oxides in batteries, 2−5 catalysis, 2,6−8 water treatment, 9,10 and sensors 11 have been widely explored. The importance of manganese oxides in the geochemical cycling of heavy metal ions has also been the subject of numerous studies given their high adsorption capacities and oxidative abilities. 12−16 β-MnO 2 (pyrolusite), a principal component in alkaline batteries, 3,4 is the most stable and abundant polymorph of manganese dioxide. 1 As such, it can be expected to play a nontrivial role in geochemical processes. β-MnO 2 is a rutiletype mineral formed from edge-sharing chains of Mn 4+ O 6 octahedra linked via their corners. It is found in the P4 2 / mnm space group with lattice constants a = 4.4041 Å and c = 2.8765 Å. 17 Natural β-MnO 2 is usually pseudomorphous after γ-MnOOH. Several transmission electron microscopy reports noted the presence of cracks parallel to the {010} planes 18,19 or rhombic holes 20 in pseudomorphous pyrolusite, which were proposed to result from the transformation of γ-MnOOH into β-MnO 2 . These structural characteristics of natural pyrolusite provide large surface area and high reactivity, 18 likely increasing its role in geochemical processes. Its specific interactions with environmental contaminants (or reactants in catalytic applications) depend on the relevant surface structure and composition under environmental conditions because these aspects of the surface influence its reactivity. Yet, structural analyses of β-MnO 2 surfaces have been few, resulting in a lack of knowledge about its surface chemistry and possible modes of interaction with adsorbates.To date, β-MnO 2 surface studies have mostly focused on the surface composition by identifying the manganese oxidation state and oxygen species present via X-ray photoelectron spectroscopy (XPS). Oku et al. 21 and Rosso and Hochella 22 examined powdered samples in UHV and found Mn 4+ and O 2− at the surface. Rosso and Hochella also noted two additional peaks in the O 1s spectra at 530.75 and 532.75 eV, which were labeled "adventitious species" and may have been due to adsorbed water or hydroxy...

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Section: ■ Methodsmentioning

confidence: 99%

Structure and Stability of Hydrated β-MnO₂ Surfaces

Oxford

Chaka

2012

J. Phys. Chem. C

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“…This value is similar to those found in other DFT studies. 39,41 To correct for this error, 0.90 eV was added to the DFT total energy of the O 2 molecule, as has been done in previous work. 39,58 The use of an O 2 energy correction here leads to an overestimation of ΔH f by 10.2%, indicating that the errors in the MnO 2 and R-Mn energies cancel some of the error in the O 2 energy.…”

Section: ' Introductionmentioning

confidence: 99%

“…39,41 To correct for this error, 0.90 eV was added to the DFT total energy of the O 2 molecule, as has been done in previous work. 39,58 The use of an O 2 energy correction here leads to an overestimation of ΔH f by 10.2%, indicating that the errors in the MnO 2 and R-Mn energies cancel some of the error in the O 2 energy. However, as noted by Franchini et al, 49 an O 2 energy correction generally improves agreement between calculated and experimental formation energies of manganese oxides.…”

Section: ' Introductionmentioning

confidence: 99%

First-Principles Calculations of Clean, Oxidized, and Reduced β-MnO₂ Surfaces

Oxford

Chaka

2011

J. Phys. Chem. C

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Manganese oxides and hydroxides are found in many geological settings and occur in the form of more than 30 minerals. 1 They participate in a variety of redox and acid/base reactions in the environment because they form interfacial barriers on soils and sediments in marine and freshwater environments and on rock and other mineral surfaces. The ability of manganese oxides to adsorb and oxidize heavy metal pollutants, such as chromium and arsenic, has been recognized for decades. Because of their ubiquity in the environment and their reactivity, these minerals serve as an important control in regulating the concentrations of groundwater contaminants. Manganese oxides are also commercially relevant as the cathode material in alkaline batteries 2,3 and have been studied for use in catalytic applications 4À6 and water treatment media. 7,8 Their redox behavior indicates that manganese oxides may potentially act as sensors as well. 9 Despite the importance of manganese oxides in geochemical processes and in technological applications, their surface structures and properties have not been well studied. For example, recent reports indicate that manganese oxides can oxidize Cr III to toxic Cr VI10À17 and toxic As III to As V . 18À22 Although these studies aimed at understanding the role of manganese oxides in the oxidation of heavy metals, it remains unclear which manganese species participate in the process and which manganese oxide surfaces are relevant for redox chemistry. A fundamental knowledge of the surface structures and their redox properties at environmentally relevant conditions is the necessary groundwork to be laid before complex interactions between heavy metal ions and manganese oxide surfaces can be fully delineated.A small number of studies have examined manganese oxide surfaces. The earliest work demonstrated reduction 23 and oxidation 24 of manganese oxide surfaces using X-ray photoelectron spectroscopy (XPS). The surface structures, however, were not characterized in either study. More recently, Langell et al. 25 examined the MnO (100) surface using high-resolution electron energy loss spectroscopy (EELS) and showed that oxidation of the surface leads to the formation of Mn 2 O 3 and subsequently Mn 3 O 4 . Intermixture of the oxide species prevented isolation of pure-phase layers and hence structural determination of the surface. EELS in scanning transmission electron microscopy was also used to analyze manganese valence at the surfaces of natural manganese oxides. 26 It was found that the average valence at the β-MnO 2 surface was 4.0, in agreement with the formal ABSTRACT: Stoichiometric and defective terminations of the β-MnO 2 (110), (100), and (101) surfaces are investigated as a function of oxygen partial pressure and temperature using ab initio thermodynamics. In agreement with studies on other rutile-type minerals, the (110) surface is predicted to be the most stable surface, followed by the (100) surface and then the (101) surface. The (110) and (101) surfaces are found to oxidize by formation...

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“…Treating the O2 molecule with U p not only helps the cancellation of errors but also addresses the well-known over-binding problem of GGA in the O2 molecule 37,243 . As discussed previously 244 , the DFT-GGA error in O2 does not cancel out in the energy sums and differences used in the ab initio thermodynamics framework. In the present work, we note that when U p is applied to the O2 the atomization energy error is reduced from 20% to 6%.…”

Section: Surface-phase Diagramsmentioning

confidence: 93%

“…We define the oxygen-poor limit based on the equilibrium of LiCoO2 = Li + Co + O2 is the total energy of a single LiCoO2 unit. In previous theoretical studies using this thermodynamic approach, the oxides studied contain only one metal species231,244,357 , and the other chemical potentials can all be related to μO. In the case of LiCoO2 where there are two metal species, one of them becomes an additional variable in the phase diagram.…”

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Extending accurate density functional modeling for the study of interface reactivity and environmental applications

Xu¹

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To my parents, Fangyan and Xingcheniii ACKNOWLEDGEMENTS Seven years in the University of Iowa have become an amazing chapter in my life.I want to express my gratitude to all the people who have helped and encouraged me during this wonderful journey. And among them all, I would like to thank my advisor, Sara E.Mason, for taking a chance to accept me and opening the entire new world of computational chemistry for me. I could never imagine that I can work on so many challenging projects.Your patience, enthusiasm and trust are not just helping me in my academic progress, but also making me grow up through all the ups and downs. I greatly appreciate your guidance and all of the opportunities to reach out in my graduate career.are not just providing the opportunities for us to apply our computational expertise in solving problems in reality, but also letting us understand the structural and chemical complexity of materials under real conditions that pushed our theoretical models to new levels. Our collaborations have built up current and future directions for our projects, and also provided more prospects in bigger academic communities. I am also thankful for the previous members of the Mason group: Dr. Sai Kumar Ramadugu, Dr. Katie Corum, and Dr. Diane Neff, you were extremely helpful for teaching me the knowledge of quantum theory and computational skills, as well as our collaborations in many different projects. iv I would also like to thank our research specialist: Dr. Joseph W. Bennett, for your in-depth understanding of materials and computational chemistry, and your tireless support for the entire group in every aspect. I am not only making academic progress by learning from your knowledge and experience, but also learning how to become a responsible and competent collaborator in team work, and deal with all the obstacles and setbacks during research. I would further like to thank all the group members, Jennifer, Diamond, Irene, Sidney and Blake, for your support and encouragement. It was a great pleasure to work with all of you. Finally, I want to thank my parents, who were thousands miles away, living on the other side of the Pacific Ocean. I just briefly spent about a month with them during my graduate years, but they provided unconditional love and support to me all the time. You constantly believed in me and encouraged my pursuits. I am eternally grateful. v ABSTRACTDensity functional theory (DFT) has become the most widely used first-principles computational method to simulate different atomic, molecular, and solid phase systems based on the electron density assumptions. The complexity of describing a many-body system has been significantly reduced in DFT. However, it also brings in potential error when dealing with a system that involves the interactions between metallic and nonmetallic species. DFT tends to overly-delocalize the electrons in metallic species and sometimes results in the overestimation of reaction energy, metallic properties in insulators, and predicts relative surface stabilities incorre...

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Publisher's Note: Density functional theory study of clean, hydrated, and defective alumina(11¯02)surfaces [Phys. Rev. B81, 125423 (2010)]

Cited by 14 publications

References 0 publications

Structure and Stability of Hydrated β-MnO₂ Surfaces

Structure and Stability of Hydrated β-MnO₂ Surfaces

First-Principles Calculations of Clean, Oxidized, and Reduced β-MnO₂ Surfaces

Extending accurate density functional modeling for the study of interface reactivity and environmental applications

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Publisher's Note: Density functional theory study of clean, hydrated, and defective alumina(11¯02)surfaces [Phys. Rev. B81, 125423 (2010)]

Cited by 14 publications

References 0 publications

Structure and Stability of Hydrated β-MnO2 Surfaces

Structure and Stability of Hydrated β-MnO2 Surfaces

First-Principles Calculations of Clean, Oxidized, and Reduced β-MnO2 Surfaces

Extending accurate density functional modeling for the study of interface reactivity and environmental applications

Contact Info

Product

Resources

About

Structure and Stability of Hydrated β-MnO₂ Surfaces

Structure and Stability of Hydrated β-MnO₂ Surfaces

First-Principles Calculations of Clean, Oxidized, and Reduced β-MnO₂ Surfaces