33 research outputs found
Operando XANES from first-principles and its application to iridium oxide
Efficient electro-catalytic water-splitting technologies require suitable
catalysts for the oxygen evolution reaction (OER). The development of novel
catalysts could benefit from the achievement of a complete understanding of the
reaction mechanism on iridium oxide (IrO), an active catalyst material that
is, however, too scarce for large-scale applications. Considerable insight has
already been provided by \emph{operando} X-ray absorption near-edge structure
(XANES) experiments, which paved the way towards an atomistic description of
the catalyst's evolution in a working environment. We combine here
first-principles simulations augmented with a continuum description of the
solvent and electrolyte to investigate the electrochemical stability of various
IrO interfaces and to predict the XANES cross-section for selected
terminations under realistic conditions of applied potential. The comparison of
computed O K-edge XANES spectra to corresponding experiments supports the
formation of electron-deficient surface oxygen species in the OER-relevant
voltage regime. Furthermore, surface hydroxyl groups that are found to be
stable up to 1 V are suggested to be progressively oxidized at larger
potentials, giving rise to a shift in the Ir L-edge cross-section that
qualitatively agrees with measurements
Effect of surface motion on the rotational quadrupole alignment parameter of D 2 reacting on Cu(111)
Ab initio molecular dynamics (AIMD) calculations using the specific reaction parameter approach to density functional theory are presented for the reaction of D2 on Cu(111) at high surface temperature (Ts = 925 K). The focus is on the dependence of reaction on the alignment of the molecule’s angular momentum relative to the surface. For the two rovibrational states for which measured energy resolved rotational quadrupole alignment parameters are available, and for the energies for which statistically accurate rotational quadrupole alignment parameters could be computed, statistically significant results of our AIMD calculations are that, on average, (i) including the effect of the experimental surface temperature (925 K) in the AIMD simulations leads to decreased rotational quadrupole alignment parameters, and (ii) including this effect leads to increased agreement with experimentC. DÃaz gratefully acknowledges support under MICINN project FIS2010-15127 and CAM program NANOBIOMAGNET S2009/MAT1726. B. Jackson gratefully acknowledges support from the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, U. S. Department of Energy, under Grant No. DE-FG02-87ER1374
An In Situ Surface-Enhanced Infrared Absorption Spectroscopy Study of Electrochemical CO2 Reduction: Selectivity Dependence on Surface C-Bound and O-Bound Reaction Intermediates
The CO_{2} electro-reduction reaction (CORR) is a promising avenue to convert
greenhouse gases into high-value fuels and chemicals, in addition to being an
attractive method for storing intermittent renewable energy. Although
polycrystalline Cu surfaces have long known to be unique in their capabilities
of catalyzing the conversion of CO_{2} to higher-order C1 and C2 fuels, such as
hydrocarbons (CH_{4}, C_{2}H_{4} etc.) and alcohols (CH_{3}OH, C_{2}H_{5}OH),
product selectivity remains a challenge. In this study, we select three metal
catalysts (Pt, Au, Cu) and apply in situ surface enhanced infrared absorption
spectroscopy (SEIRAS) and ambient-pressure X-ray photoelectron spectroscopy
(APXPS), coupled to density-functional theory (DFT) calculations, to get
insight into the reaction pathway for the CORR. We present a comprehensive
reaction mechanism for the CORR, and show that the preferential reaction
pathway can be rationalized in terms of metal-carbon (M-C) and metal-oxygen
(M-O) affinity. We show that the final products are determined by the
configuration of the initial intermediates, C-bound and O-bound, which can be
obtained from CO_{2} and (H)CO_{3}, respectively. C1 hydrocarbons are produced
via OCH_{3, ad} intermediates obtained from O-bound CO_{3, ad} and require a
catalyst with relatively high affinity for O-bound intermediates. Additionally,
C2 hydrocarbon formation is suggested to result from the C-C coupling between
C-bound CO_{ad} and (H)CO_{ad}, which requires an optimal affinity for the
C-bound species, so that (H)CO_{ad} can be further reduced without poisoning
the catalyst surface. Our findings pave the way towards a design strategy for
CORR catalysts with improved selectivity, based on this
experimental/theoretical reaction mechanisms that have been identified
Solvent-aware Interfaces in Continuum Solvation
Continuum models to handle solvent and electrolyte effects in an effective
way have a long tradition in quantum-chemistry simulations and are nowadays
also being introduced in computational condensed-matter and materials
simulations. A key ingredient of continuum models is the choice of the solute
cavity, i.e. the definition of the sharp or smooth boundary between the regions
of space occupied by the quantum-mechanical (QM) system and the continuum
embedding environment. Although most of the solute-based approaches developed
lead to models with comparable and high accuracy when applied to small organic
molecules, they can introduce significant artifacts when complex systems are
considered. As an example, condensed-matter simulations often deal with
supports that present open structures. Similarly, unphysical pockets of
continuum solvent may appear in systems featuring multiple molecular
components. Here, we introduce a solvent-aware approach to eliminate the
unphysical effects where regions of space smaller than the size of a single
solvent molecule could still be filled with a continuum environment. We do this
by defining a smoothly varying solute cavity that overcomes several of the
limitations of straightforward solute-based definitions. This new approach
applies to any smooth local definition of the continuum interface, being it
based on the electronic density or the atomic positions of the QM system. It
produces boundaries that are continuously differentiable with respect to the QM
degrees of freedom, leading to accurate forces and/or Kohn-Sham potentials.
Benchmarks on semiconductor substrates and on explicit water substrates confirm
the flexibility and the accuracy of the approach and provide a general set of
parameters for condensed-matter systems featuring open structures and/or
explicit liquid components
CGC: a scalable Python package for co- and tri-clustering of geodata cubes
Clustering Geo-Data Cubes (CGC) is a Python package to perform clustering analysis for multidimensional geospatial data. The included tools allow the user to efficiently run tasks in parallel on local and distributed systems
Application of van der Waals functionals to the calculation of dissociative adsorption of N 2
Theoretical Chemistr
Fast and Credible Likelihood-Free Cosmology with Truncated Marginal Neural Ratio Estimation
Sampling-based inference techniques are central to modern cosmological data
analysis; these methods, however, scale poorly with dimensionality and
typically require approximate or intractable likelihoods. In this paper we
describe how Truncated Marginal Neural Ratio Estimation (TMNRE) (a new approach
in so-called simulation-based inference) naturally evades these issues,
improving the efficiency, scalability, and trustworthiness
of the inferred posteriors. Using measurements of the Cosmic Microwave
Background (CMB), we show that TMNRE can achieve converged posteriors using
orders of magnitude fewer simulator calls than conventional Markov Chain Monte
Carlo (MCMC) methods. Remarkably, the required number of samples is effectively
independent of the number of nuisance parameters. In addition, a property
called \emph{local amortization} allows the performance of rigorous statistical
consistency checks that are not accessible to sampling-based methods. TMNRE
promises to become a powerful tool for cosmological data analysis, particularly
in the context of extended cosmologies, where the timescale required for
conventional sampling-based inference methods to converge can greatly exceed
that of simple cosmological models such as CDM. To perform these
computations, we use an implementation of TMNRE via the open-source code
\texttt{swyft}.Comment: v2: accepted journal version. v1: 37 pages, 13 figures.
\texttt{swyft} is available at https://github.com/undark-lab/swyft, and
demonstration code for cosmological examples is available at
https://github.com/acole1221/swyft-CM
Methane dissociation on Pt(111): Searching for a specific reaction parameter density functional
Theoretical Chemistr