Center for Molecular Modeling - A. Van Yperen-De Deyne

Ab initio study of the trapping of polonium on noble metals

andy — Tue, 29 Sep 2015 19:41:29 +0000

K. Rijpstra, A. Van Yperen-De Deyne, E. A. Maugeri, J. Neuhausen, M. Waroquier, V. Van Speybroeck, S. Cottenier

Journal of Nuclear Materials

472, 35-42

2016

Abstract

In the future MYRRHA reactor, lead bismuth eutectic (LBE) will be used both as coolant and as spallation target. Due to the high neutron flux a small fraction of the bismuth will transmute to radiotoxic ²¹⁰Po. Part of this radiotoxic element will evaporate into the gas above the coolant. Extracting it from the gas phase is necessary to ensure a safe handling of the reactor. An issue in the development of suitable filters is the lack of accurate knowledge on the chemical interaction between a candidate filter material and either elemental polonium or polonium containing molecules. Experimental work on this topic is complicated by the high radiotoxicity of polonium. Therefore, we present in this paper a first-principles study on the adsorption of polonium on noble metals as filter materials. The adsorption of monoatomic Po is considered on the candidate filter materials palladium, platinum, silver and gold. The case of the gold filter is looked upon in more detail by examining how bismuth pollution affects its capability to capture polonium and by studying the adsorption of the heavy diatomic molecules Po₂, PoBi and PoPb on this gold filter.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1016/j.jnucmat.2016.01.026

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JNuclMat_Rijpstra_coauthor-version_2015-07-09(1).pdf

Vibrational fingerprint of the absorption properties of UiO-type MOF materials

andy — Wed, 16 Sep 2015 12:38:04 +0000

A. Van Yperen-De Deyne, K. Hendrickx, L. Vanduyfhuys, G. Sastre, P. Van der Voort, V. Van Speybroeck, K. Hemelsoet

Theoretical Chemistry Accounts

135, 4, 102

2016

Abstract

The absorption properties of UiO-type metal–organic frameworks are computed using TD-DFT simulations on the organic linkers. A set of nine isoreticular structures, including the UiO-66 and UiO-67 materials and functionalized variants, are examined. The excitation energies from a static geometry optimization are compared with dynamic averages obtained from sampling the ground-state potential energy surface using molecular dynamics. The vibrational modes that impact the excitation energy are identified. This analysis is done using a recently proposed tool based on power spectra of the velocities and the excitation energies. The applied procedure allows including important factors influencing the absorption spectra, such as the periodic framework, linker variation and dynamical effects including harmonic and anharmonic nuclear motions. This methodology allows investigating in detail the vibrational fingerprint of the excitation energy of advanced materials such as MOFs and gives perspectives to tailor materials toward new light-based applications.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1007/s00214-016-1842-8

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16-TheorChemAcc-135-102-VanYperenDeDeyne.pdf

Understanding Intrinsic Light Absorption Properties of UiO- 66 Frameworks: A Combined Theoretical and Experimental Study

kevin — Fri, 21 Aug 2015 15:49:51 +0000

K. Hendrickx, D.E.P. Vanpoucke, K. Leus, K. Lejaeghere, A. Van Yperen-De Deyne, V. Van Speybroeck, P. Van der Voort, K. Hemelsoet

Inorganic Chemistry

54, 22, 10701-10710

2015

Abstract

A combined theoretical and experimental study is performed in order to elucidate the effects of linker functional groups on the photoabsorption properties of UiO-66-type materials. This study, in which both mono- and di-functionalized linkers (with X= -OH, -NH2, -SH) are studied, aims to obtain a more complete picture on the choice of functionalization. Static Time-Dependent Density Functional Theory (TD-DFT) calculations combined with Molecular Dynamics simulations are performed on the linkers and compared to experimental UV/VIS spectra, in order to understand the electronic effects governing the absorption spectra. Di-substituted linkers show larger shifts compared to mono-substituted variants, making them promising candidates for further study as photocatalysts. Next, the interaction between the linker and the inorganic part of the framework is theoretically investigated using a cluster model. The proposed Ligand-to-Metal-Charge Transfer (LMCT) is theoretically observed and is influenced by the differences in functionalization. Finally, computed electronic properties of the periodic UiO-66 materials reveal that the band gap can be altered by linker functionalization and ranges from 4.0 down to 2.2 eV. Study of the periodic Density of States (DOS) allows to explain the band gap modulations of the framework in terms of a functionalization-induced band in the band gap of the original UiO-66 host.

DOI

http://dx.doi.org/10.1021/acs.inorgchem.5b01593

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Determination of the Nature of the Cu coordination complexes formed in the presence of NO and NH3 within SSZ-13

michel — Thu, 20 Aug 2015 10:26:17 +0000

I. Lezcano-Gonzalez, D. Wragg, W. A. Slawinski, K. Hemelsoet, A. Van Yperen-De Deyne, M. Waroquier, V. Van Speybroeck, A. Beale

Journal of Physical Chemistry C

119 (43), 24393-24403

2015

Abstract

Ammonia-selective catalytic reduction (NH3-SCR) using Cu zeolites is a well-established strategy for the abatement of NOx gases. Recent studies have demonstrated that Cu is particularly active when exchanged into the SSZ-13 zeolite, and its location in either the 6r or 8r renders it an excellent model system for fundamental studies. In this work, we examine the interaction of NH3-SCR relevant gases (NO and NH3) with the Cu2+ centers within the SSZ-13 structure, coupling powder diffraction (PD), X-ray absorption spectroscopy (XAFS), and density functional theory (DFT). This combined approach revealed that, upon calcination, cooling and gas exposure Cu ions tend to locate in the 8r window. After NO introduction, Cu ions are seen to coordinate to two framework oxygens and one NO molecule, resulting in a bent Cu–nitrosyl complex with a Cu–N–O bond angle of ∼150°. Whilst Cu seems to be partially reduced/changed in coordination state, NO is partially oxidized. On exposure to NH3 while the PD data suggest the Cu2+ ion occupies a similar position, simulation and XAFS pointed toward the formation of a Jahn–Teller distorted hexaamine complex [Cu(NH3)6]2+ in the center of the cha cage. These results have important implications in terms of uptake and storage of these reactive gases and potentially for the mechanisms involved in the NH3-SCR process.

DOI

http://dx.doi.org/10.1021/acs.jpcc.5b06875

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Determination of the Nature of the Cu Coordination Complexes Formed in the Presence of NO and NH3 within SSZ-13

michel — Wed, 22 Jul 2015 14:08:03 +0000

I. Lezcano-Gonzalez, D. Wragg, W. A. Slawinski, K. Hemelsoet, A. Van Yperen-De Deyne, M. Waroquier, V. Van Speybroeck

Journal of Physical Chemistry C

2015

Published while none of the authors were employed at the CMM

DOI

http://dx.doi.org/

Binary and Ternary Po-containing Molecules Relevant for LBE Cooled Reactors at Operating Temperature

michel — Fri, 18 Jul 2014 08:09:21 +0000

A. Van Yperen-De Deyne, K. Rijpstra, M. Waroquier, V. Van Speybroeck, S. Cottenier

Journal of Nuclear Materials

458, 288-295

2015

Abstract

Quantum-chemical calculations at several levels of theory were used to assess the stability at different temperatures of a set of 13 binary and ternary Po-containing molecules that could possibly be formed in an environment with lead, bismuth, oxygen and water. The conclusions are that especially PoPb, PbPoO and PoOH and to a lesser extent Po2 and PoO are stable. These small molecules are therefore likely to be found near the Lead-Bismuth eutectic (LBE) coolant at operational temperatures in a heavy liquid metal cooled fission reactor. In contrast, Po3 and PoBi are unlikely to be present under the assumed conditions. Several stability criteria, such as the dissociation into free atoms or into molecular fragments at realistic Po-concentrations or in the thermodynamic limit are discussed at different temperatures. The results obtained with a medium level of theory (Density Functional Theory, PBE0 with relativistic effective core potentials) show good qualitative correspondence with calculations performed at a much higher level of theory (Multi Reference Configuration Interaction, with spin–orbit coupling and scalar relativistic Hamiltonian).

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1016/j.jnucmat.2014.11.064

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Automated generation of radical species in crystalline carbohydrate using ab initio MD simulations

michel — Mon, 16 Jun 2014 19:21:40 +0000

S.G. Aalbergsjø, E. Pauwels, A. Van Yperen-De Deyne, V. Van Speybroeck, E. Sagstuen

Physical Chemistry Chemical Physics (PCCP)

16 (32), 17196-17205

2014

Abstract

As the chemical structures of radiation damaged molecules may vary greatly from their undamaged counterparts, investigation and description of radiation damaged structures is commonly biased by the researcher. Radical formation from ionizing radiation in crystalline α-L-rhamnose monohydrate has been investigated using a new method where the selection of radical structures is unbiased by the researcher. The method is based on using ab initio molecular dynamics (MD) studies to investigate how ionization damage can form, change and move. Diversity in the radical production is gained by using different points on the potential energy surface of the intact crystal as starting points for the ionizations and letting the initial velocities of the nuclei after ionization be generated randomly. 160 ab initio MD runs produced 12 unique radical structures for investigation. Out of these, 7 of the potential products have never previously been discussed, and 3 products are found to match with radicals previously observed by electron magnetic resonance experiments

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1039/C4CP02179G

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Exploring the Vibrational Fingerprint of the Electronic Excitation Energy via Molecular Dynamics

michel — Tue, 26 Nov 2013 20:29:14 +0000

A. Van Yperen-De Deyne, T. De Meyer, E. Pauwels, A. Ghysels, K. De Clerck, M. Waroquier, V. Van Speybroeck, K. Hemelsoet

Journal of Chemical Physics

140 (2014), 134105

2014

Abstract

A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitation energy computed using time-dependent density functional theory. Peaks in both spectra are compared, and motions exhibiting a linear or quadratic behavior can be distinguished. The quadratically active motions are mainly responsible for the changes in the excitation energy and hence cause shifts between the dynamic and static values of the spectral property. Moreover, information about the potential energy surface of various excited states can be obtained. The procedure is illustrated with three case studies. The first electronic excitation is explored in detail and dominant vibrational motions responsible for changes in the excitation energy are identified for ethylene, biphenyl, and hexamethylbenzene. The proposed method is also extended to other low-energy excitations. Finally, the vibrational fingerprint of the excitation energy of a more complex molecule, in particular the azo dye ethyl orange in a water environment, is analyzed.

DOI

http://dx.doi.org/10.1063/1.4869937

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Mn-salen@MIL101(Al) a heterogeneous, enantioselective catalyst using a ‘bottle around the ship’ approach

bogaerts — Tue, 09 Jul 2013 09:43:07 +0000

T. Bogaerts, A. Van Yperen-De Deyne, Y-Y Liu, F. Lynen, V. Van Speybroeck, P. Van der Voort

Chemical Communications

2013 (49), 8021-8023

2013

Abstract

An enantioselective catalyst, consisting of a chiral Mn(III)salen complex entrapped in the MIL-101 metal organic framework is reported. For the first time, we assemble a robust MOF-cage around a delicate chiral complex, without affecting the structure and stability of this complex. The newly prepared heterogeneous catalyst shows the same enantioselective excess compared to the homogeneous Mn(III)salen complex and is fully recyclable. Theoretical calculations yield insight into the dimensions of the various transition states of the epoxidation reaction.

DOI

http://dx.doi.org/10.1039/C3CC44473B

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Solution Enthalpy of Po and Te in solid Lead-Bismuth Eutectic

wim — Tue, 02 Jul 2013 13:08:58 +0000

K. Rijpstra, A. Van Yperen-De Deyne, J. Neuhausen, V. Van Speybroeck, S. Cottenier

Journal of Nuclear Materials

450 (1–3), 287–291

2014

Abstract

It is examined to which extent ﬁrst-principles calculations can be used to collect a priori information on the solution enthalpy and solubility of Po in solid lead-bismuth eutectic (LBE). Such information can be helpful to limit the number of complicated experiments that are required to measure these properties. It is found that in the thermodynamic limit and at 0 K, Po does not dissolve in solid LBE. Its solution enthalpy is negative, in particular in Pb-rich environments, but competing compound-forming reactions are more exothermic. A clear correlation is found between the calculated solution enthalpies for Te in LBE and for Po in LBE, suggesting that Te-experiments can be used to map the expected behaviour for Po. The role of spin-orbit coupling as the major relativistic eﬀect on the solution enthalpies of these heavy atoms is inspected.

DOI

http://dx.doi.org/10.1016/j.jnucmat.2013.07.004

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