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Isseroff L.Y.,Princeton University | Carter E.A.,Andlinger Center for Energy and the Environment
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We show that a "one-shot" GW approach (denoted G 0W 0) can accurately calculate the photoemission/inverse- photoemission properties of Cu 2O. As the results of any perturbative method are heavily dependent on the reference state, the appropriate reference Hamiltonian for G 0W 0 is identified by evaluating the performance of density-functional-theory-based input wave functions and eigenvalues generated with selected exchange-correlation functionals. It is shown that a reference Hamiltonian employing the hybrid Heyd-Scuseria-Ernzerhof functional used in conjunction with G 0W 0 produces an accurate photoemission/inverse-photoemission band gap and photoemission spectrum whose character is then further analyzed. The physical origin of why a hybrid functional is required for the zeroth-order wave function is discussed, giving insight into the unique electronic structure of Cu 2O in comparison to other transition-metal oxides. © 2012 American Physical Society. Source

Libisch F.,Vienna University of Technology | Huang C.,Los Alamos National Laboratory | Carter E.A.,Andlinger Center for Energy and the Environment
Accounts of Chemical Research | Year: 2014

ConspectusAb initio modeling of matter has become a pillar of chemical research: with ever-increasing computational power, simulations can be used to accurately predict, for example, chemical reaction rates, electronic and mechanical properties of materials, and dynamical properties of liquids. Many competing quantum mechanical methods have been developed over the years that vary in computational cost, accuracy, and scalability: density functional theory (DFT), the workhorse of solid-state electronic structure calculations, features a good compromise between accuracy and speed. However, approximate exchange-correlation functionals limit DFT's ability to treat certain phenomena or states of matter, such as charge-transfer processes or strongly correlated materials. Furthermore, conventional DFT is purely a ground-state theory: electronic excitations are beyond its scope. Excitations in molecules are routinely calculated using time-dependent DFT linear response; however applications to condensed matter are still limited.By contrast, many-electron wavefunction methods aim for a very accurate treatment of electronic exchange and correlation. Unfortunately, the associated computational cost renders treatment of more than a handful of heavy atoms challenging. On the other side of the accuracy spectrum, parametrized approaches like tight-binding can treat millions of atoms. In view of the different (dis-)advantages of each method, the simulation of complex systems seems to force a compromise: one is limited to the most accurate method that can still handle the problem size. For many interesting problems, however, compromise proves insufficient. A possible solution is to break up the system into manageable subsystems that may be treated by different computational methods. The interaction between subsystems may be handled by an embedding formalism.In this Account, we review embedded correlated wavefunction (CW) approaches and some applications. We first discuss our density functional embedding theory, which is formally exact. We show how to determine the embedding potential, which replaces the interaction between subsystems, at the DFT level. CW calculations are performed using a fixed embedding potential, that is, a non-self-consistent embedding scheme. We demonstrate this embedding theory for two challenging electron transfer phenomena: (1) initial oxidation of an aluminum surface and (2) hot-electron-mediated dissociation of hydrogen molecules on a gold surface. In both cases, the interaction between gas molecules and metal surfaces were treated by sophisticated CW techniques, with the remainder of the extended metal surface being treated by DFT. Our embedding approach overcomes the limitations of conventional Kohn-Sham DFT in describing charge transfer, multiconfigurational character, and excited states. From these embedding simulations, we gained important insights into fundamental processes that are crucial aspects of fuel cell catalysis (i.e., O2 reduction at metal surfaces) and plasmon-mediated photocatalysis by metal nanoparticles. Moreover, our findings agree very well with experimental observations, while offering new views into the chemistry. We finally discuss our recently formulated potential-functional embedding theory that provides a seamless, first-principles way to include back-action onto the environment from the embedded region. © 2014 American Chemical Society. Source

Shin I.,Princeton University | Carter E.A.,Andlinger Center for Energy and the Environment
International Journal of Plasticity | Year: 2014

The strength and ductility of metals are governed by the motion of dislocations, which is quantified by the Peierls stress (σp). We use orbital-free density functional theory (OFDFT) to characterize the motion of 13〈112̄0〉 dislocations on the basal {0001} and prismatic {11̄00} planes in hexagonal-close-packed magnesium (Mg) in order to understand its deformation mechanisms. We predict σp values of edge dislocations on the basal and prismatic planes to be 0.6 and 35.4 MPa, respectively. The presence of stable stacking faults only on the basal plane produces partial dislocation splitting, which significantly lowers σp for basal dislocations. Our atomic scale simulations reveal that dislocation mobility is strongly correlated with the number of core atoms moving collectively. OFDFT σp results are in excellent agreement with experiments (∼0.5 and 39.2 MPa), further validating OFDFT as an independent and predictive tool for simulating plastic behavior in main group metals at the mesoscale with first principles' accuracy. © 2014 Elsevier Ltd. All rights reserved. Source

Liao P.,Princeton University | Keith J.A.,Princeton University | Carter E.A.,Princeton University | Carter E.A.,Andlinger Center for Energy and the Environment
Journal of the American Chemical Society | Year: 2012

In photoelectrochemical cells, sunlight may be converted into chemical energy by splitting water into hydrogen and oxygen molecules. Hematite (α-Fe 2O 3) is a promising photoanode material for the water oxidation component of this process. Numerous research groups have attempted to improve hematite's photocatalytic efficiency despite a lack of foundational knowledge regarding its surface reaction kinetics. To elucidate detailed reaction mechanisms and energetics, we performed periodic density functional theory + U calculations for the water oxidation reaction on the fully hydroxylated hematite (0001) surface. We investigate two different concentrations of surface reactive sites. Our best model involves calculating water oxidation mechanisms on a pure (1× 1) hydroxylated hematite slab (corresponding to 1/3 ML of reactive sites) with an additional overlayer of water molecules to model solvation effects. This yields an overpotential of 0.77 V, a value only slightly above the 0.5-0.6 V experimental range. To explore whether doped hematite can exhibit an even lower overpotential, we consider cation doping by substitution of Fe by Ti, Mn, Co, Ni, or Si and F anion doping by replacing O on the fully hydroxylated surface. The reaction energetics on pure or doped hematite surfaces are described using a volcano plot. The relative stabilities of holes on the active O anions are identified as the underlying cause for trends in energetics predicted for different dopants. We show that moderately charged O anions give rise to smaller overpotentials. Co- or Ni-doped hematite surfaces give the most thermodynamically favored reaction pathway (lowest minimum overpotential) among all dopants considered. Very recent measurements (Electrochim. Acta2012, 59, 121-127) reported improved reactivity with Ni doping, further validating our predictions. © 2012 American Chemical Society. Source

van der Linden S.,Andlinger Center for Energy and the Environment | Maibach E.,George Mason University | Leiserowitz A.,Yale University
Perspectives on Psychological Science | Year: 2015

Despite being one of the most important societal challenges of the 21st century, public engagement with climate change currently remains low in the United States. Mounting evidence from across the behavioral sciences has found that most people regard climate change as a nonurgent and psychologically distant risk—spatially, temporally, and socially—which has led to deferred public decision making about mitigation and adaptation responses. In this article, we advance five simple but important “best practice” insights from psychological science that can help governments improve public policymaking about climate change. Particularly, instead of a future, distant, global, nonpersonal, and analytical risk that is often framed as an overt loss for society, we argue that policymakers should (a) emphasize climate change as a present, local, and personal risk; (b) facilitate more affective and experiential engagement; (c) leverage relevant social group norms; (d) frame policy solutions in terms of what can be gained from immediate action; and (e) appeal to intrinsically valued long-term environmental goals and outcomes. With practical examples we illustrate how these key psychological principles can be applied to support societal engagement and climate change policymaking. © 2015, The Author(s) 2015. Source

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