133 research outputs found
A first-principles tool to discover new pyrometallurgical refining options
No full textWe demonstrate the opportunities of first-principles density functional theory (DFT) calculations for the development of new metallurgical refining processes. As such, a methodology based on DFT calculations is developed to discover new pyrometallurgical refining processes that use the addition of a third element to remove an impurity from a molten host material. As a case study, this methodology is applied to the refining of lead. The proposed method predicts the existing refining routes as well as alternative processes. The most interesting candidate for the removal of arsenic from lead is experimentally verified, which confirms the suitability of the remover element. The method is therefore considered as a useful approach to speed up the discovery of new pyrometallurgical refining processes, as it provides an ordered set of interesting candidate remover elements.sponsorship: Computational resources have been provided by the supercomputing facilities of the Universite catholique de Louvain (CISM/UCL) and the Consortium des Equipements de Calcul Intensif en Federation Wallonie Bruxelles (CECI) funded by the Fonds de la Recherche Scientifique de Belgique (FRS-FNRS). Funding via the Agency for Innovation and Entrepreneurship (VLAIO) project HBC.2016.0733 of the Flemish region with Campine is acknowledged. (Fonds de la Recherche Scientifique de Belgique (FRS-FNRS), Agency for Innovation and Entrepreneurship (VLAIO)|HBC.2016.0733)status: Publishe
Improving Accuracy and Transferability of Machine Learning Chemical Activation Energies by Adding Electronic Structure Information
No full textBenchmarking First-Principles Reaction Equilibrium Composition Prediction
No full textThe availability of thermochemical properties allows for the prediction of the equilibrium compositions of chemical reactions. The accurate prediction of these can be crucial for the design of new chemical synthesis routes. However, for new processes, these data are generally not completely available. A solution is the use of thermochemistry calculated from first-principles methods such as Density Functional Theory (DFT). Before this can be used reliably, it needs to be systematically benchmarked. Although various studies have examined the accuracy of DFT from an energetic point of view, few studies have considered its accuracy in predicting the temperature-dependent equilibrium composition. In this work, we collected 117 molecules for which experimental thermochemical data were available. From these, we constructed 2648 reactions. These experimentally constructed reactions were then benchmarked against DFT for 6 exchange–correlation functionals and 3 quality of basis sets. We show that, in reactions that do not show temperature dependence in the equilibrium composition below 1000 K, over 90% are predicted correctly. Temperature-dependent equilibrium compositions typically demonstrate correct qualitative behavior. Lastly, we show that the errors are equally caused by errors in the vibrational spectrum and the DFT electronic ground state energy
Core-Level Binding Energies from GW: An Efficient Full-Frequency Approach within a Localized Basis
No full textThe GW method is routinely used to predict charged valence excitations in molecules and solids. However, the numerical techniques employed in the most efficient GW algorithms break down when computing core excitations as measured by X-ray photoelectron spectroscopy (XPS). We present a full-frequency approach on the real axis using a localized basis to enable the treatment of core levels in GW. Our scheme is based on the contour deformation technique and allows for a precise and efficient calculation of the selfenergy, which has a complicated pole structure for core states. The accuracy of our method is validated by comparing to a fully analytic GW algorithm. Furthermore, we report the obtained core-level binding energies and their deviations from experiment for a set of small molecules and large polycyclic hydrocarbons. The core-level excitations computed with our GW approach deviate by less than 0.5 eV from the experimental reference. For comparison, we also report core-level binding energies calculated by density functional theory (DFT)-based approaches such as the popular delta self-consistent field (ΔSCF) method. Our implementation is optimized for massively parallel execution, enabling the computation of systems up to 100 atoms
Modeling X-ray Photoelectron Spectroscopy of Macromolecules Using <i>GW</i>
No full textWe propose a simple additive approach to simulate X-ray photoelectron spectra (XPS) of macromolecules based on the GW method. Single-shot GW (G0W0) is a promising technique to compute accurate core-electron binding energies (BEs). However, its application to large molecules is still unfeasible. To circumvent the computational cost of G0W0, we break the macromolecule into tractable building blocks, such as isolated monomers, and sum up the theoretical spectra of each component, weighted by their molar ratio. In this work, we provide a first proof of concept by applying the method to four test polymers and one copolymer and show that it leads to an excellent agreement with experiments. The method could be used to retrieve the composition of unknown materials and study chemical reactions, by comparing the simulated spectra with experimental ones.sponsorship: The authors thank Paul van der Heide (Imec) for fruitful discussions. The authors acknowledge funding from the Imec Industrial Affiliation Program (IIAP) . (Imec Industrial Affiliation Program (IIAP))status: Published onlin
Computing elastic tensors of amorphous materials from first-principles
No full textThe resources and services used in this work were partly provided by the VSC (Flemish Supercomputer Center) , funded by the Research Foundation-Flanders (FWO) and the Flemish Government. The various members of our group for discussions and aid over the course of this research
A First-Principles Investigation of the Driving Forces Defining the Selectivity of TiO2 Atomic Layer Deposition
No full textThe GW miracle: Many-body perturbation theory for the ionization potential of molecule
No full textInternational audienceWe use the GW100 benchmark set to systematically judge the quality of several perturbation theories against high-level quantum chemistry methods.First of all, we revisit the reference CCSD(T) ionization potentials for this popular benchmark set and establish a revised set of CCSD(T) results.Then, for all of these 100 molecules, we calculate the HOMO energy within second- and third-order perturbation theory (PT2 and PT3), and as post Hartree-Fock methods. is by far the most accurate approximation for the ionization potential.Going beyond by adding more diagrams is a tedious and dangerous activity: We tried to complement with second-order exchange (SOX), with second-order screened exchange (SOSEX), with interacting electron-hole pairs (), and with a density-matrix (). Only the result has a positive impact. Finally using an improved hybrid functional for the non-interacting Green's function, considering it as a cheap way to approximate self-consistency, the accuracy of the simplest approximation improves even more. We conclude that is a miracle: The neglected diagrams compensate almost perfectly, which makes both accurate and fast
Influence of NOx on soot combustion with supported molten salt catalysts
No full textDiesel soot is combusted simultaneously by two reactions: combustion with NO2 and combustion with O-2 with the aid of a molten salt catalyst. Both reaction pathways should always be considered to avoid misinterpretation of experimental data
On the elastic tensors of ultra-thin films: A study of ruthenium
No full textThe resources and services used in this work were partly provided by the VSC (Flemish Supercomputer Center) , funded by the Research Foundation-Flanders (FWO) , Belgium and the Flemish Government, Belgium. The various members of our group for discussions and aid over the course of this research
- …
