628 research outputs found
Thermodynamics of water modeled using ab initio simulations
We regularize the potential distribution framework to calculate the excess
free energy of liquid water simulated with the BLYP-D density functional. The
calculated free energy is in fair agreement with experiments but the excess
internal energy and hence also the excess entropy are not. Our work emphasizes
the importance of thermodynamic characterization in assessing the quality of
electron density functionals in describing liquid water and hydration
phenomena
Improved coupled perturbed Hartree–Fock and Kohn–Sham convergence acceleration
A derivative version of the well-known direct inversion in the iterative subspace (DIIS) algorithm is presented. The method is used to solve the coupled perturbed Hartree–Fock (CPHF) equation to obtain the first and second derivatives of the density matrix with respect to an external electric field which, in this case, leads to the electric molecular polarizability and hyperpolarizability. Some comparisons are presented and the method shows good convergences in almost all cases
Molecular packing and chemical association in liquid water simulated using ab initio hybrid Monte Carlo and different exchange-correlation functionals
In the free energy of hydration of a solute, the chemical contribution is
given by the free energy required to expel water molecules from the
coordination sphere and the packing contribution is given by the free energy
required to create the solute-free coordination sphere (the observation volume)
in bulk water. With the SPC/E water model as a reference, we examine the
chemical and packing contributions in the free energy of water simulated using
different electron density functionals. The density is fixed at a value
corresponding to that for SPC/E water at a pressure of 1 bar. The chemical
contribution shows that water simulated at 300 K with BLYP is somewhat more
tightly bound than water simulated at 300 K with the revPBE functional or at
350 K with the BLYP and BLYP-D functionals. The packing contribution for
various radii of the observation volume is studied. In the size range where the
distribution of water molecules in the observation volume is expected to be
Gaussian, the packing contribution is expected to scale with the volume of the
observation sphere. Water simulated at 300 K with the revPBE and at 350 K with
BLYP-D or BLYP conforms to this expectation, but the results suggest an earlier
onset of system size effects in the BLYP 350 K and revPBE 300 K systems than
that observed for either BLYP-D 350 K or SPC/E. The implication of this
observation for constant pressure simulations is indicated. For water simulated
at 300 K with BLYP, in the size range where Gaussian distribution of occupation
is expected, we instead find non-Gaussian behavior, and the packing
contribution scales with surface area of the observation volume, suggesting the
presence of heterogeneities in the system
Comparison of computational methods for the electrochemical stability window of solid-state electrolyte materials
Superior stability and safety are key promises attributed to all-solid-state
batteries (ASSBs) containing solid-state electrolyte (SSE) compared to their
conventional counterparts utilizing liquid electrolyte. To unleash the full
potential of ASSBs, SSE materials that are stable when in contact with the low
and high potential electrodes are required. The electrochemical stability
window is conveniently used to assess the SSE-electrode interface stability. In
the present work, we review the most important methods to compute the SSE
stability window. Our analysis reveals that the stoichiometry stability method
represents a bridge between HOMO-LUMO method and phase stability method (grand
canonical phase diagram). Moreover, we provide computational implementations of
these methods for SSE material screening. We compare their results for the
relevant Li- and Na-SSE materials LGPS, LIPON, LLZO, LLTO, LATP, LISICON, and
NASICON, and we discuss their relation to published experimental stability
windows
A particle finite element-based model for droplet spreading analysis
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Mahrous, Elaf, et al. “A Particle Finite Element-Based Model for Droplet Spreading Analysis.” Physics of Fluids, vol. 32, no. 4, American Institute of Physics, Apr. 2020, p. 42106, doi:10.1063/5.0006033. and may be found at https://aip.scitation.org/doi/abs/10.1063/5.0006033A particle finite element method-based model is proposed to analyze droplet dynamics problems, particularly droplet spreading on solid substrates (wetting). The model uses an updated Lagrangian framework to formulate the governing equations of the liquid. The curvature of the liquid surface is tracked accurately using a deforming boundary mesh. In order to predict the spreading rate of the droplet on the solid substrate and track the corresponding contact angle evolution, dissipative forces at the contact line are included in the formulation in addition to the Navier-slip boundary conditions at the solid–liquid interface. The inclusion of these boundary conditions makes it possible to account for the induced Young’s stress at the contact line and for the viscous dissipation along the solid–liquid interfacial region. These are found to be essential to obtain a mesh-independent physical solution. The temporal evolution of the contact angle and the contact line velocity of the proposed model are compared with spreading droplets and micro-sessile droplet injection experiments and are shown to be in good agreement.We are grateful to Dr. Howard Stone, Dr. James Bird, and Dr. Shreyas Mandre for their permission to use Fig. 11(a) published in Ref. 53. We thank the reviewers for their feedback and constructive comments. E.M. is thankful to Dr. Ajay Prasad for the fruitful discussion about the effect of shear stresses on droplet spreading phenomena. E.M. acknowledges the financial support by Jubail University College and the Royal Commission for Jubail and Yanbu of Saudi Arabia. M.S. and A.J. acknowledge financial support from the Natural Science and Engineering Research Council of Canada (NSERC) Collaborative Research and Development, Grant No. NSERC CRDPJ 445887-12, and the NSERC Discovery grant. P.R. was supported by the AMADEUS project (Grant No. PGC2018- 101655-B-I00) funded by the Spanish Ministry of Science, Innovation and Universities. T.C. and A.Z.W. acknowledge financial support by the Fuel Cell Performance and Durability Consortium (FC-PAD) and by the Fuel Cell Technologies Office (FCTO), Office of Energy Efficiency and Renewable Energy (EERE), of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231.Peer ReviewedPostprint (author's final draft
Ab initio linear scaling response theory: Electric polarizability by perturbed projection
A linear scaling method for calculation of the static {\em ab inito} response
within self-consistent field theory is developed and applied to calculation of
the static electric polarizability. The method is based on density matrix
perturbation theory [Niklasson and Challacombe, cond-mat/0311591], obtaining
response functions directly via a perturbative approach to spectral projection.
The accuracy and efficiency of the linear scaling method is demonstrated for a
series of three-dimensional water clusters at the RHF/6-31G** level of theory.
Locality of the response under a global electric field perturbation is
numerically demonstrated by approximate exponential decay of derivative density
matrix elements.Comment: 4.25 pages in PRL format, 2 figure
Boron: A key element in radical reactions
Boron derivatives are becoming key reagents in radical chemistry. Here, we describe reactions where an organoboron derivative is used as a radical initiator, a chain-transfer reagent, and a radical precursor. For instance, B-alkylcatecholboranes, easily prepared by hydroboration of alkenes, represent a very efficient source of primary, secondary, and tertiary alkyl radicals. Their very high sensitivity toward oxygen- and heteroatom-centered radicals makes them particularly attractive for the development of radical chain processes such as conjugate addition, allylation, alkenylation, and alkynylation. Boron derivatives have also been used to develop an attractive new procedure for the reduction of radicals with alcohols and water. The selected examples presented here demonstrate that boron-containing reagents can efficiently replace tin derivatives in a wide range of radical reaction
- …