Center for Molecular Modeling - FWO NANO (3G076012) B/12578/*

Synergistic Effects in the Activity of Nano-Transition-Metal clusters Pt12M (M = Ir, Ru or Rh) for NO dissociation

jvekeman — Tue, 14 Jun 2022 14:24:32 +0000

J. Vekeman, Q. Wang, X. Deraet, D. Bazin, F. De Proft, H. Guesmi, F. Tielens

ChemPhysChem

23, 21, e202200740

2022

Abstract

The dissociation of environmentally hazardous NO through dissociative adsorption on metallic clusters supported by oxides, is receiving growing attention. Building on previous research on monometallic M 13 clusters [J. Phys. Chem. C, 2019, 123(33), 20314-20318], this work considers bimetallic Pt 12 M (M = Rh, Ru or Ir) clusters. The adsorption energy and activation energy of NO dissociation on the clusters have been calculated in vacuum using Koh,-Sham DFT, while their trends were rationalized using reactivity indices such as molecular electrostatic potential and global Fermi softness. The results shown that doping of the Pt clusters lowered the adsorption energy as well as the activation energy for NO dissociation. Furthermore, reactivity indices were calculated as a first estimate of the performance of the clusters in realistic amorphous silica pores (MCM-41) through ab initio molecular dynamics simulations.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1002/cphc.202200740

Mechanistic Insights in Seeded Growth Synthesis of Colloidal Core/Shell Quantum Dots

msluydts — Fri, 19 May 2017 19:01:55 +0000

I. Nakonechnyi, M. Sluydts, Y. Justo, J. Jasieniak, Z. Hens

Chemistry of Materials

29 (11), 4719-4727

2017

Abstract

We analyze the mechanism of seeded growth reactions used to synthesize colloidal core/shell nanocrystals. Looking at the formation of CdSe/CdS and CdSe/ZnSe using both zinc blende and wurtzite CdSe seeds with a different surface termination, we show that the formation rate of the shell material does not depend on the presence of the CdSe seed nanocrystals. This suggests that shells grow by inclusion of CdS or ZnSe initially formed in the reaction mixture, possibly under the form of reactive monomers, and not by successive adsorption and reaction of metal and chalcogen precursors. This insight makes balancing homogeneous nucleation and heterogeneous growth of the shell material key to suppressing spurious secondary nucleation. Through a combination of experimental work and reaction simulations, we show that this can be effectively achieved by raising the monomer solubility through the concentration of carboxylic acid used in the seeded growth reaction.

DOI

http://dx.doi.org/10.1021/acs.chemmater.7b00354

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acs.chemmater.7b00354.pdf

High-Throughput Screening of Extrinsic Point Defect Properties in Si and Ge: Database and Applications

msluydts — Fri, 13 Jan 2017 09:58:24 +0000

M. Sluydts, M. Pieters, J. Vanhellemont, V. Van Speybroeck, S. Cottenier

Chemistry of Materials

29 (3), pp 975–984

2016

Abstract

Increased computational resources now make it possible to generate large data sets solely from first principles. Such “high-throughput” screening is employed to create a database of embedding enthalpies for extrinsic point defects and their vacancy complexes in Si and Ge for 73 impurities from H to Rn. Calculations are performed both at the PBE and HSE06 levels of theory. The data set is verified by comparison of the predicted lowest-enthalpy positions with experimental observations. The effect of temperature on the relative occupation of defect sites is estimated through configurational entropy. Potential applications are demonstrated by selecting optimal vacancy traps, directly relevant to industrial processes such as Czochralski growth as a means to suppress void formation.

DOI

http://dx.doi.org/10.1021/acs.chemmater.6b03368

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acs%2Echemmater%2E6b03368.pdf

Error estimates for density-functional theory predictions of surface energy and work function

kurt — Sat, 24 Sep 2016 09:52:20 +0000

S. De Waele, K. Lejaeghere, M. Sluydts, S. Cottenier

Physical Review B

Vol. 94, Iss. 23 — 15 December 2016

2016

Abstract

Density-functional theory (DFT) predictions of materials properties are becoming ever more widespread. With increased use comes the demand for estimates of the accuracy of DFT results. In view of the importance of reliable surface properties, this work calculates surface energies and work functions for a large and diverse test set of crystalline solids. They are compared to experimental values by performing a linear regression, which results in a measure of the predictable and material-specific error of the theoretical result. Two of the most prevalent functionals, the local density approximation (LDA) and the Perdew-Burke-Ernzerhof parametrization of the generalized gradient approximation (PBE-GGA), are evaluated and compared. Both LDA and GGA-PBE are found to yield accurate work functions with error bars below 0.3 eV, rivaling the experimental precision. LDA also provides satisfactory estimates for the surface energy with error bars smaller than 10%, but GGA-PBE significantly underestimates the surface energy for materials with a large correlation energy.

Open Access version available at UGent repository

DOI

https://doi.org/10.1103/PhysRevB.94.235418

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PhysRevB.94.235418.pdf

Towards metal–organic framework based field effect chemical sensors: UiO-66-NH2 for nerve agent detection

michel — Sat, 09 Jul 2016 19:53:21 +0000

L. Stassen, B. Bueken, H. Reinsch, J.F.M. Oudenhoven, D. Wouters, J. Hajek, V. Van Speybroeck, N. Stock, P.M. Vereecken, R. Van Schajik, D. De Vos, R. Ameloot

Chemical Science

7, 5827-5832

2016

Abstract

We present a highly sensitive gas detection approach for the infamous ‘nerve agent’ group of alkyl phosphonate compounds. Signal transduction is achieved by monitoring the work function shift of metal–organic framework UiO-66-NH2 coated electrodes upon exposure to ppb-level concentrations of a target simulant. Using the Kelvin probe technique, we demonstrate the potential of electrically insulating MOFs for integration in field effect devices such as ChemFETs: a three orders of magnitude improvement over previous work function-based detection of nerve agent simulants. Moreover, the signal is fully reversible both in dry and humid conditions, down to low ppb concentrations. Comprehensive investigation of the interactions that lead towards this high sensitivity points towards a series of confined interactions between the analyte and the pore interior of UiO-66-NH₂.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1039/C6SC00987E

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c6sc00987e.pdf

Ligand Addition Energies and the Stoichiometry of Colloidal Nanocrystals

msluydts — Wed, 30 Dec 2015 08:55:46 +0000

M. Sluydts, K. De Nolf, V. Van Speybroeck, S. Cottenier, Z. Hens

ACS Nano

10 (1), 1462-1474

2016

Abstract

Experimental non-stoichiometries of colloidal nanocrystals such as CdSe and PbS are accounted for by attributing to each constituent atom and capping ligand a formal charge equal to its most common oxidation state to obtain an overall neutral nanocrystal. In spite of its apparent simplicity, little theoretical support of this approach - called here the oxidation-number sum rule - is present in the current literature. Here, we introduce the ligand addition energy, which we define as the energy gained or expended upon the transfer of one ligand from a reference state to a (metal-rich) solid surface. For the combination of CdSe, ZnSe and InP with either chalcogen, halogen or hydrochalcogen ligands, we compute successive ligand addition energies using ab initio methods and determine the thermodynamically stable surface composition as that composition where ligand addition turns endothermic. We find that the oxidation-number sum rule is valid in many situations, although exceptions occur for each material studied most notably when exposed to small oxidative ligands. In the case of InP violations are more severe, extending towards the entire chalcogen ligand family. In addition, we find that electronegativity rather than chemical hardness is a reasonable predictor for ligand addition energies, with the most electronegative ligands yielding the most exothermic addition energies. Finally, we argue that the ligand addition energy will be a most useful quantity for future computational studies on the structure, stability and reactivity of nanocrystal surfaces.

DOI

http://dx.doi.org/10.1021/acsnano.5b06965

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16-ACSNano-10(1)1462-Sluydts.pdf

On the stability and nature of adsorbed pentene in Brønsted acid zeolite H-ZSM-5 at 323 K

kristof — Wed, 20 May 2015 14:41:23 +0000

J. Hajek, J. Van der Mynsbrugge, K. De Wispelaere, P. Cnudde, L. Vanduyfhuys, M. Waroquier, V. Van Speybroeck

Journal of Catalysis

340, 227 - 235

2016

Abstract

Adsorption of linear pentenes in H-ZSM-5 at 323 K is investigated using contemporary static and molecular dynamics methods. A physisorbed complex corresponding to free pentene, a π-complex and a chemisorbed species may occur. The chemisorbed species can be either a covalently bonded alkoxide or an ion pair, the so-called carbenium ion. Without finite temperature effects, the π-complex is systematically slightly more bound than the chemisorbed alkoxide complex, whereas molecular dynamics calculations at 323 K yield an almost equal stability of both species. The carbenium ion was not observed during simulations at 323 K. The transformation from the π-complex to the chemisorbed complex is activated by a free energy in the range of 33–42 kJ/mol. Our observations yield unprecedented insights into the stability of elusive intermediates in zeolite catalysis, for which experimental data are very hard to measure.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1016/j.jcat.2016.05.018

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1-s2.0-S0021951716300628-main.pdf

JCAT-16-151R1(1).pdf

Controlling the Size of Hot Injection Made Nanocrystals by Manipulating the Diffusion Coefficient of the Solute

wim — Tue, 28 Apr 2015 07:35:02 +0000

K. De Nolf, R.K. Capek, S. Abé, M. Sluydts, Y. Jang, J.C. Martins, S. Cottenier, E. Lifshitz, Z. Hens

JACS (Journal of the American Chemical Society)

137 (7), 2495–2505

2015

Abstract

We investigate the relation between the chain length of ligands used and the size of the nanocrystals formed in the hot injection synthesis. With two different CdSe nanocrystal syntheses, we consistently find that longer chain carboxylic acids result in smaller nanocrystals with improved size dispersions. By combining a more in-depth experimental investigation with kinetic reaction simulations, we come to the conclusion that this size tuning is due to a change in the diffusion coefficient and the solubility of the solute. The relation between size tuning by the ligand chain length and the coordination of the solute by the ligands is further explored by expanding the study to amines and phosphine oxides. In line with the weak coordination of CdSe nanocrystals by amines, no influence of the chain length on the nanocrystals is found, whereas the size tuning brought about by phosphine oxides can be attributed to a solubility change. We conclude that the ligand chain length provides a practical handle to optimize the outcome of a hot injection synthesis in terms of size and size dispersion and can be used to probe the interaction between ligands and the actual solute.

DOI

http://dx.doi.org/10.1021/ja509941g

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15_JACS_137(7)2495_DeNolf.pdf

VASP training school

wim — Wed, 11 May 2016 11:30:44 +0000

Rennes, France

Wednesday, 31 August, 2016 to Saturday, 3 September, 2016

Participant(s)

P. Cnudde, K. Lejaeghere, C. Caratelli, S. Bailleul, A. De Vos, J. Hajek

Project ref.

IAP VII P7/05 B/12909/*, BOF K. Lejaeghere BOFPDO2014001301, ERC DYNPOR H20ERC2015000301, FWO NANO (3G076012) B/12578/*, DEFNET (641887) H20ITN2015000201

Conference reference

VASP training school

Shape tuning of CdSe nanostructures by ab initio determination of the anisotropic growth mechanism.

msluydts — Mon, 29 Feb 2016 08:54:19 +0000

Description

Abstract zie PDF.

Feedback:

‘This is a well-written (short but to-the-point) proposal about understanding the growth mechanism of CdSe nanocrystals. This results in tunable optical behavior which is relevant for LEDs and LASERs where the color of the emitted light can be varied. It is decomposed in 3 phases, the first one is screening of the ligand surrounding the nanocrystals and the second and third ones are the most computational intensive (relaxation and frequency).
All 3 mandated persons have at least 4 years experience on Tier 2 and Tier 1.
The scaling curves are shown for each phase for the CdSe surface and the number of nodes is chosen accordingly: both to the scalability capability but also in respect to the number of k-points. At 3 nodes, they get 85% of the ideal speedup and at 9 nodes, they still get 60% which is still acceptable.
The applicants use self-developed management software that track consumed resources and can gradually increase accuracy settings to limit unnecessary resource consumption. Using this software, the number of nodes per task will be tuned to 2 – 4 nodes.’

Budget/project

FWO NANO (3G076012) B/12578/*

Period

Friday, 26 February, 2016 to Wednesday, 31 August, 2016

Node days

4 752.00 days

Users

M. Sluydts, V. Van Speybroeck, S. Cottenier

Remaining days

4 752.00 days

Downloads

TIER1_Feb2016_MichaelSluydts_Final.pdf

TIER1 reference n°

2016-2

Status

Approved