scholarly journals Self-organization of extraframework cations in zeolites

2012 ◽  
Vol 468 (2143) ◽  
pp. 2070-2086 ◽  
Author(s):  
Evgeny A. Pidko ◽  
Emiel J. M. Hensen ◽  
Rutger A. van Santen
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Metal Species ◽  
Binuclear Complexes ◽  
Specific Distribution ◽  
Equivalent Number ◽  
Fe Complexes ◽  
High Silica ◽  
The Stability ◽  
Extraframework Cations

Structural properties of a series of mordenite and ZSM-5 zeolites with different framework Al distribution modified with oxygenated extraframework Ga, Zn, Al, Cu and Fe complexes were investigated by means of periodic density functional theory calculations. It is demonstrated that mononuclear oxygenated and hydroxylated cationic metal complexes in high-silica zeolites tend to self-organize into binuclear complexes. In the cases of Ga- and Fe-modified zeolites, it is shown that the catalytic activity of the most stable binuclear extraframework cations is much higher than that of the hypothetical very reactive mononuclear counterparts. This is due to a weaker binding of reaction intermediates and easier regeneration of the initial active complexes in the course of the catalytic reaction. The formation of multiple-charged binuclear oxygenated metal species in zeolites is a general phenomenon. It does not require a specific distribution of the equivalent number of negative framework charges that compensate for the positive charge of the cationic complexes. The location and the stability of cationic complexes in zeolite micropores are mainly determined by the coordination properties of the metal centres.

Targeting complex plutonium oxides by combining crystal chemical reasoning with density-functional theory calculations: the quaternary plutonium oxide Cs2PuSi6O15

2020 ◽  
Vol 56 (66) ◽  
pp. 9501-9504
Author(s):  
Kristen A. Pace ◽  
Vladislav V. Klepov ◽  
Matthew S. Christian ◽  
Gregory Morrison ◽  
Travis K. Deason ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Crystal Growth ◽  
Dft Calculations ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Crystal Chemical ◽  
The Novel ◽  
Functional Theory ◽  
The Stability ◽  
Chemical Reasoning

The stability of the novel Pu(iv) silicate, Cs2PuSi6O15, was predicted from a combination of crystal chemical reasoning and DFT calculations and confirmed by its synthesis via flux crystal growth.

scholarly journals Computational Modeling of Tensile Stress Effects on the Structure and Stability of Prototypical Covalent and Layered Materials

Nanomaterials ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1483 ◽  
Author(s):  
Hocine Chorfi ◽  
Álvaro Lobato ◽  
Fahima Boudjada ◽  
Miguel A. Salvadó ◽  
Ruth Franco ◽  
...  
Keyword(s):  
Tensile Stress ◽  
Density Functional ◽  
Stability Limit ◽  
Density Functional Theory Calculations ◽  
Layered Materials ◽  
Stress Conditions ◽  
Ideal Strength ◽  
Critical Strength ◽  
Calculated Stress ◽  
The Stability

Understanding the stability limit of crystalline materials under variable tensile stress conditions is of capital interest for technological applications. In this study, we present results from first-principles density functional theory calculations that quantitatively account for the response of selected covalent and layered materials to general stress conditions. In particular, we have evaluated the ideal strength along the main crystallographic directions of 3C and 2H polytypes of SiC, hexagonal ABA stacking of graphite and 2H-MoS 2 . Transverse superimposed stress on the tensile stress was taken into account in order to evaluate how the critical strength is affected by these multi-load conditions. In general, increasing transverse stress from negative to positive values leads to the expected decreasing of the critical strength. Few exceptions found in the compressive stress region correlate with the trends in the density of bonds along the directions with the unexpected behavior. In addition, we propose a modified spinodal equation of state able to accurately describe the calculated stress–strain curves. This analytical function is of general use and can also be applied to experimental data anticipating critical strengths and strain values, and for providing information on the energy stored in tensile stress processes.

DFT STUDIES ON THE STABILITY OF THE TRANS AND CIS ISOMERS IN THE SQUARE PLANAR PALLADIUM(II) COMPLEXES Pd(I)(PPh3)(η3-XCHC(Ph)CHR) (X = CMe3, CO2Me, P(O)(OMe)2, AND SO2H; R = H, Me)

2008 ◽  
Vol 07 (04) ◽  
pp. 505-515
Author(s):  
LIQIN XUE ◽  
GUOCHEN JIA ◽  
ZHENYANG LIN
Keyword(s):  
Density Functional Theory ◽  
Electronic Properties ◽  
Relative Stability ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Dft Studies ◽  
Functional Theory ◽  
Square Planar ◽  
The Stability ◽  
Cis Isomer

The relative stability of the trans and cis isomers in the square planar palladium(II) complexes Pd ( I )( PPh 3)(η3- XCHC ( Ph ) CHR ) ( X = H , Me , CMe 3, CO 2 Me , P ( O )( OMe )2, and SO 2 H ; R = H , Me ) was investigated with the aid of the B3LYP density functional theory calculations. We examined how the substituents X, with different electronic properties, of the η3-allyl ligands affect the relative stability of the trans and cis isomers. Through the investigation, we were able to explain the trans/cis relative stability derived from the experimentally measured trans/cis isomer ratios in the palladium(II) complexes.

Exploring halide anion affinities to native cyclodextrins by mass spectrometry and molecular modelling

2017 ◽  
Vol 24 (3) ◽  
pp. 269-278 ◽  
Author(s):  
Chongsheng Xu ◽  
Nan He ◽  
Zhenhua Li ◽  
Yanqiu Chu ◽  
Chuan-Fan Ding
Keyword(s):  
Gas Phase ◽  
Density Functional ◽  
Binding Constants ◽  
Density Functional Theory Calculations ◽  
Collision Induced Dissociation ◽  
Binding Affinities ◽  
Cyclodextrin Complex ◽  
Halide Anion ◽  
Mass Frame ◽  
The Stability

The binding affinities of cyclodextrins complexation with chlorine (Cl−), bromine (Br−) and iodine (I−), were measured by mass spectrometric titrimetry, and the fitting of the binding constants was based on the concentration measurement of the cyclodextrin equilibrium. The binding constants (lg Ka) for α-, β- or γ-cyclodextrin with Cl− were 3.99, 4.03 and 4.11, respectively. The gas-phase binding affinity of halide anions for native cyclodextrins was probed by collision-induced dissociation. In collision-induced dissociation, the centre-of-mass frame energy results revealed that in the gas phase, for the same type of cyclodextrin, the stability of the complexes decreased in order: Cl > Br > I, and for the same halide anion, the binding stability of the complex with α-, β- or γ-cyclodextrin decreased in the order: γ-cyclodextrin >β-cyclodextrin > α-cyclodextrin. The density functional theory calculations showed that halide anion binding on the primary face had a lower energy than the secondary face and hydrogen bonding was the main driving force for complex formation. The higher stability of the γ-cyclodextrin complex with the Cl anion can be attributed to the higher charge density of the Cl anion and better flexibility of γ-cyclodextrin.

Stability, Electronic Properties, and Structural Isomerism in Small Copper Clusters

2012 ◽  
Vol 1479 ◽  
pp. 15-20
Author(s):  
Juan M. Montejano-Carrizales ◽  
Faustino Aguilera-Granja ◽  
Ricardo A. Guirado-López
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Three Dimensional ◽  
Density Functional Theory Calculations ◽  
Energy Barriers ◽  
Elastic Band ◽  
Experimental Conditions ◽  
Atomic Displacements ◽  
Structural Isomerism ◽  
The Stability

ABSTRACTWe present extensive pseudopotential density functional theory calculations dedicated to analyze the stability, electronic properties, and structural isomerism in Cu6 clusters. We consider structures of different symmetries and charge states. Our total energy calculations reveal a strong competition between two- and three-dimensional atomic arrays, the later being mostly energetically preferred for the anionic structures. The bond lengths and electronic spectra strongly depend on the local atomic environment, a result that is expected to strongly influence the catalytic activity of our clusters. Using the nudged elastic band method we analyze the interconversion processes between different Cu6 isomers. Complex atomic relaxations are obtained when we study the transition between different cluster structures; however relatively small energy barriers of approximately 0.3 eV accompany the atomic displacements. Interestingly, we obtain that by considering positively charged Cu6+ systems we reduce further the energy barriers opposing the interconversion process. The previous results could imply that, under a range of experimental conditions, it should be possible to observe different Cu6cluster structures in varying proportions.

Density Functional Theory Calculations of Properties of the Grain Boundaries in Aluminum

2011 ◽  
Vol 1297 ◽  
Author(s):  
Marek Muzyk ◽  
Krzysztof J. Kurzydlowski
Keyword(s):  
Density Functional Theory ◽  
Grain Boundaries ◽  
Density Functional ◽  
Quantitative Description ◽  
Aluminum Matrix ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Nano Crystalline ◽  
The Density Functional Theory ◽  
The Stability

ABSTRACTThe Density Functional Theory has been used to analyze an inter-granular segregation of Cu and Mg. The stability of Cu and Mg atoms in the aluminum matrix, intermetallic phases and symmetric twist grain boundaries has been compared. The quantitative description of solubility of Cu and Mg atoms in the nano-crystalline aluminum has been proposed. The calculations have been carried out to investigate the properties of symmetric twist boundaries in aluminum with and without Cu/Mg atoms. The phenomena of are discussed and its effect on the stability of precipitates containing these elements.

scholarly journals Substituent effects in the decarboxylation reactions of coordinated arylcarboxylates in dinuclear copper complexes, [(napy)Cu2(O2CC6H4X)]+

2017 ◽  
Vol 23 (6) ◽  
pp. 351-358 ◽  
Author(s):  
Qiuyan Jin ◽  
Jiaye Li ◽  
Alireza Ariafard ◽  
Allan J Canty ◽  
Richard AJ O’Hair
Keyword(s):  
Density Functional Theory ◽  
Transition State ◽  
Density Functional ◽  
Copper Complexes ◽  
Substituent Effects ◽  
Density Functional Theory Calculations ◽  
Molecular Formula ◽  
Binuclear Complexes ◽  
Aryl Group ◽  
Functional Theory

A combination of gas-phase ion trap mass spectrometry experiments and density functional theory (DFT) calculations have been used to examine the role of substituents on the decarboxylation of 25 different coordinated aromatic carboxylates in binuclear complexes, [(napy)Cu2(O2CC6H4X)]+, where napy is the ligand 1,8-naphthyridine (molecular formula, C8H6N2) and X = H and the ortho ( o), meta ( m) and para ( p) isomers of F, Br, CN, NO2, CF3, OAc, Me and MeO. Two competing unimolecular reaction pathways were found: decarboxylation to give the organometallic cation [(napy)Cu2(C6H4X)]+ or loss of the neutral copper benzoate to yield [(napy)Cu]+. The substituents on the aryl group influence the branching ratios of these product channels, but decarboxylation is always the dominant pathway. Density functional theory calculations reveal that decarboxylation proceeds via two transition states. The first enables a change in the coordination mode of the coordinated benzoate in [(napy)Cu2(O2CC6H4X)]+ from the thermodynamically favoured O, O-bridged form to the O-bound form, which is the reactive conformation for the second transition state which involves extrusion of CO2 with concomitant formation of the CO2 coordinated organometallic cation, [(napy)Cu2(C6H4X)(CO2)]+, which then loses CO2 in the final step to yield [(napy)Cu2(C6H4X)]+. In all cases the barrier is highest for the second transition state. The o-substituted benzoates show a lower activation energy than the m-substituted ones, while the p-substituted ones have the highest energy, which is consistent with the experimentally determined normalised collision energy required to induce fragmentation of [(napy)Cu2(O2CC6H4X)]+.

scholarly journals Pressure-induced phase transitions in Na2B12H12, structural investigation on a candidate for solid-state electrolyte

2019 ◽  
Vol 75 (3) ◽  
pp. 406-413 ◽  
Author(s):  
Romain Moury ◽  
Zbigniew Łodziana ◽  
Arndt Remhof ◽  
Léo Duchêne ◽  
Elsa Roedern ◽  
...  
Keyword(s):  
High Pressure ◽  
Solid State ◽  
Bulk Modulus ◽  
Density Functional ◽  
Ambient Pressure ◽  
Density Functional Theory Calculations ◽  
Ionic Conductors ◽  
Theoretical Predictions ◽  
Primary Order ◽  
The Stability

closo-Borates, such as Na2B12H12, are an emerging class of ionic conductors that show promising chemical, electrochemical and mechanical properties as electrolytes in all-solid-state batteries. Motivated by theoretical predictions, high-pressure in situ powder X-ray diffraction on Na2B12H12 was performed and two high-pressure phases are discovered. The first phase transition occurs at 0.5 GPa and it is persistent to ambient pressure, whereas the second transition takes place between 5.7 and 8.1 GPa and it is fully reversible. The mechanisms of the transitions by means of group theoretical analysis are unveiled. The primary-order parameters are identified and the stability at ambient pressure of the first polymorph is explained by density functional theory calculations. Finally, the parameters relevant to engineer and build an all-solid-state battery, namely, the bulk modulus and the coefficient of the thermal expansion are reported. The relatively low value of the bulk modulus for the first polymorph (14 GPa) indicates a soft material which allows accommodation of the volume change of the cathode during cycling.

scholarly journals Advanced study of hydrogen storage by substitutional doping of Mn and Ti in Mg2Ni phase

2014 ◽  
Vol 5 ◽  
pp. A24 ◽  
Author(s):  
Omar Elkedim ◽  
Liwu Huang ◽  
David Bassir
Keyword(s):  
Density Functional Theory ◽  
Hydrogen Storage ◽  
First Principles ◽  
Density Functional ◽  
Lattice Site ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Substitutional Doping ◽  
The Stability ◽  
Ti Substitution

The substitutional doping of Mn and Ti in Mg2Ni phase has been investigated by first principles density functional theory calculations. The calculation of enthalpy of formation shows that among the four different lattice sites of Mg(6f), Mg(6i), Ni(3b) and Ni(3d) in Mg2Ni unit cell, the most preferable site of substitution of Mn in Mg2Ni lattice has been confirmed to be Mg(6i) lattice site. The most preferable site of Ti substitution in Mg2Ni lattice is Mg(6i) position and the stability of Ti-doped Mg2Ni decreases with the increase of substitution quantity of Ti for Mg.

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