scholarly journals Chemical ordering in substituted fluorite oxides: a computational investigation of Ho2Zr2O7 and RE2Th2O7 (RE=Ho, Y, Gd, Nd, La)

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Jonathan M. Solomon ◽  
Jacob Shamblin ◽  
Maik Lang ◽  
Alexandra Navrotsky ◽  
Mark Asta
Keyword(s):  
Dft Calculations ◽  
Density Functional ◽  
Waste Containment ◽  
Chemical Ordering ◽  
Oxygen Coordination ◽  
Vacancy Ordering ◽  
Trivalent Cations ◽  
Yield Values ◽  
Scattering Study ◽  
The Stability

Abstract Fluorite-structured oxides find widespread use for applications spanning nuclear energy and waste containment, energy conversion, and sensing. In such applications the host tetravalent cation is often partially substituted by trivalent cations, with an associated formation of charge-compensating oxygen vacancies. The stability and properties of such materials are known to be influenced strongly by chemical ordering of the cations and vacancies, and the nature of such ordering and associated energetics are thus of considerable interest. Here we employ density-functional theory (DFT) calculations to study the structure and energetics of cation and oxygen-vacancy ordering in Ho2Zr2O7. In a recent neutron total scattering study, solid solutions in this system were reported to feature local chemical ordering based on the fluorite-derivative weberite structure. The calculations show a preferred chemical ordering qualitatively consistent with these findings, and yield values for the ordering energy of 9.5 kJ/mol-cation. Similar DFT calculations are applied to additional RE2Th2O7 fluorite compounds, spanning a range of values for the ratio of the tetravalent and trivalent (RE) cation radii. The results demonstrate that weberite-type order becomes destabilized with increasing values of this size ratio, consistent with an increasing energetic preference for the tetravalent cations to have higher oxygen coordination.

scholarly journals A density functional study on the reactivity enhancement induced by gold in IrAu nanoalloys

RSC Advances ◽  
2018 ◽  
Vol 8 (19) ◽  
pp. 10450-10456
Author(s):  
Paula S. Cappellari ◽  
Germán J. Soldano ◽  
Marcelo M. Mariscal
Keyword(s):  
Dft Calculations ◽  
Density Functional ◽  
Chemical Reactivity ◽  
Functional Study ◽  
Density Functional Study ◽  
Chemical Ordering ◽  
The Stability

The effects of chemical ordering on the stability and chemical reactivity on IrAu NAs of different sizes (8, 27, 48 and 64 total atoms) and compositions are studied using DFT calculations.

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.

XRD Multi-Temperatures Study of N,N'-bis(2-Hydroxyethyl)Benzene-1,4-Dicarboxamide

2010 ◽  
Vol 163 ◽  
pp. 256-259
Author(s):  
Gabriela Bednarek ◽  
Maria Nowak ◽  
Joachim Kusz ◽  
Jerzy Ossowski
Keyword(s):  
Crystal Structure ◽  
Density Functional Theory ◽  
Dft Calculations ◽  
Chemical Reactions ◽  
Title Compound ◽  
Density Functional ◽  
Temperature Analysis ◽  
Functional Theory ◽  
X Ray ◽  
The Stability

N,N’ – bis – (2– hydroxy – ethylene) – terephthalamide (BHETA) has been obtained by aminolysis of polyethylene terephthalate (PET) using excess of monoethanoloamine and it has been physicochemically characterized [1]. In this paper there are shown the results of the multi-temperature X-ray measurement which were performed to provide information about the stability of the structure. Detailed temperature analysis of the crystal structure allows us to determine properties of the compound which is very important product of recycling PET wastes in order to use it for further chemical reactions. The structure of the title compound was also modelled by density functional theory (DFT) calculations.

scholarly journals Simplifying and Expanding the Scope of Boron Imidazolate Framework (BIF) Synthesis Using Mechanochemistry

2021 ◽  
Author(s):  
Cameron Lennox ◽  
Jean-Louis Do ◽  
Joshua Crew ◽  
Mihails Arhangelskis ◽  
Hatem M. Titi ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
Density Functional ◽  
Heavy Atom ◽  
Functional Theory ◽  
Rapid Access ◽  
Solution Methods ◽  
The Stability

Mechanochemistry enables rapid access to boron imidazolate frameworks (BIFs), including ultralight materials based on Li and Cu(I) nodes, as well as new and previously unexplored systems based on Ag(I) nodes. Compared to solution methods, mechanochemistry is faster, provides materials with improved porosity, and replaces harsh reactants (e.g. n-butyllithium) with simpler and safer oxides, carbonates or hydroxides. Periodic density-functional theory (DFT) calculations on polymorphic pairs of BIFs based on Li<sup>+</sup>, Cu<sup>+</sup>, and Ag<sup>+</sup> nodes reveals that heavy-atom nodes increase the stability of the open SOD-framework relative to the non-porous <i>dia</i>-polymorph.<br>

scholarly journals Formation, Stability and Magnetism of New Gd3TAl3Ge2 Quaternary Compounds (T = Mn, Cu)

2019 ◽  
Vol 289 ◽  
pp. 93-101
Author(s):  
Manish K. Kashyap ◽  
Timothy A. Hackett ◽  
Alessia Provino ◽  
Arjun K. Pathak ◽  
Vitalij K. Pecharsky ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Density Functional ◽  
Experimental Investigations ◽  
Stable Phase ◽  
Functional Theory ◽  
Quaternary Compounds ◽  
General Chemical ◽  
Existence And Stability ◽  
The Stability ◽  
Formation Energies

A study on the formation and stability of new quaternary compounds with the general chemical formula Gd3TAl3Ge2(T = Mn, Cu) has been undertaken by experimental investigations (SEM-EDX, DTA and XRD) and density functional theory (DFT) calculations. These compounds crystallize in the hexagonal Y3NiAl3Ge2-type structure (hP9, P–62m, Z = 1) (an ordered, quaternary derivative of the ternary ZrNiAl or of the binary Fe2P prototypes), with lattice parameters values a = 7.0239(2) Å and c = 4.2580(1) Å for Gd3MnAl3Ge2and a = 7.0434(1) Å and c = 4.2089(1) Å for Gd3CuAl3Ge2. DTA suggests a peritectic reaction for the formation of these compounds (at 1245°C for Gd3CuAl3Ge2). The existence and stability of these phases has been explained on the basis of DFT calculations, and a comparison of ground state properties of the studied compounds with the earlier known Gd3CoAl3Ge2phase is outlined. The negative formation energies in all three cases govern the stability of compounds from theory as well, predicting Gd3MnAl3Ge2as the most stable phase with highest formation energy (–13.01 eV/f.u.). The total DOS are generic in nature and suggest the robust magnetism, with the Gd-f moments of ≈7 μB. An antiparallel coupling among Gd-f and T-d states is observed for all compounds, as usually seen in rare earth (R) - transition metal (T) compounds. Preliminary magnetization measurements on Gd3MnAl3Ge2show two ferromagnetic/ferrimagnetic (FM/FIM) like transitions at TC1= 142 K and TC2= 97 K, with another anomaly seen at ≈15 K. Isothermal magnetization data show no hysteresis even at 5 K, and the magnetization does not saturate up to 50 kOe, further suggesting a possible FIM behavior.

scholarly journals Simplifying and Expanding the Scope of Boron Imidazolate Framework (BIF) Synthesis Using Mechanochemistry

2021 ◽  
Author(s):  
Cameron Lennox ◽  
Jean-Louis Do ◽  
Joshua Crew ◽  
Mihails Arhangelskis ◽  
Hatem M. Titi ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
Density Functional ◽  
Heavy Atom ◽  
Functional Theory ◽  
Rapid Access ◽  
Solution Methods ◽  
The Stability

Mechanochemistry enables rapid access to boron imidazolate frameworks (BIFs), including ultralight materials based on Li and Cu(I) nodes, as well as new and previously unexplored systems based on Ag(I) nodes. Compared to solution methods, mechanochemistry is faster, provides materials with improved porosity, and replaces harsh reactants (e.g. n-butyllithium) with simpler and safer oxides, carbonates or hydroxides. Periodic density-functional theory (DFT) calculations on polymorphic pairs of BIFs based on Li<sup>+</sup>, Cu<sup>+</sup>, and Ag<sup>+</sup> nodes reveals that heavy-atom nodes increase the stability of the open SOD-framework relative to the non-porous <i>dia</i>-polymorph.<br>

scholarly journals The effect of cation–π interactions on the stability and electronic properties of anticancer drug Altretamine: a theoretical study

2020 ◽  
Vol 76 (10) ◽  
pp. 982-991
Author(s):  
Fahimeh Alirezapour ◽  
Azadeh Khanmohammadi
Keyword(s):  
Charge Transfer ◽  
Dft Calculations ◽  
Electronic Properties ◽  
Anticancer Drug ◽  
Density Functional ◽  
Nbo Analysis ◽  
Basis Set ◽  
Π Interactions ◽  
Chemical Computation ◽  
The Stability

The present work utilizes density functional theory (DFT) calculations to study the influence of cation–π interactions on the electronic properties of the complexes formed by Altretamine [2,4,6-tris(dimethylamino)-1,3,5-triazine], an anticancer drug, with mono- and divalent (Li+, Na+, K+, Be2+, Mg2+ and Ca2+) metal cations. The structures were optimized with the M06-2X method and the 6-311++G(d,p) basis set in the gas phase and in solution. The theory of `Atoms in Molecules' (AIM) was applied to study the nature of the interactions by calculating the electron density ρ(r) and its Laplacian at the bond critical points. The charge-transfer process during complexation was evaluated using natural bond orbital (NBO) analysis. The results of DFT calculations demonstrate that the strongest/weakest interactions belong to Be2+/K+ complexes. There are good correlations between the achieved densities and the amounts of charge transfer with the interaction energies. Finally, the stability and reactivity of the cation–π interactions can be determined by quantum chemical computation based on the molecular orbital (MO) theory.

Computationally Assisted Design of High Signal-to-Noise Photoinduced Electron Transfer-Based Voltage-Sensitive Dyes

2020 ◽  
Author(s):  
Rishikesh Kulkarni ◽  
Anneliese Gest ◽  
Chun Kei Lam ◽  
Benjamin Raliski ◽  
Feroz James ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Dft Calculations ◽  
Photoinduced Electron Transfer ◽  
Density Functional ◽  
Embryonic Stem ◽  
High Sensitivity ◽  
Md Simulations ◽  
High Signal ◽  
Signal To Noise ◽  
Green Fluorescent

<p>High signal-to-noise optical voltage indicators will enable simultaneous interrogation of membrane potential in large ensembles of neurons. However, design principles for voltage sensors with high sensitivity and brightness remain elusive, limiting the applicability of voltage imaging. In this paper, we use molecular dynamics (MD) simulations and density functional theory (DFT) calculations to guide the design of a bright and sensitive green-fluorescent voltage-sensitive fluorophore, or VoltageFluor (VF dye), that uses photoinduced electron transfer (PeT) as a voltage-sensing mechanism. MD simulations predict an 11% increase in sensitivity due to membrane orientation, while DFT calculations predict an increase in fluorescence quantum yield, but a decrease in sensitivity due to a decrease in rate of PeT. We confirm these predictions by synthesizing a new VF dye and demonstrating that it displays the expected improvements by doubling the brightness and retaining similar sensitivity to prior VF dyes. Combining theoretical predictions and experimental validation has resulted in the synthesis of the highest signal-to-noise green VF dye to date. We use this new voltage indicator to monitor the electrophysiological maturation of human embryonic stem cell-derived medium spiny neurons. </p>

Structure, Stability and Water Adsorption on Ultra-Thin TiO2 Supported on TiN

2019 ◽  
Author(s):  
Jose Julio Gutierrez Moreno ◽  
Marco Fronzi ◽  
Pierre Lovera ◽  
alan O'Riordan ◽  
Mike J Ford ◽  
...  
Keyword(s):  
Density Functional ◽  
Water Adsorption ◽  
Chemical Potential ◽  
Energy Gap ◽  
Molecular Water ◽  
Structure Stability ◽  
Ambient Conditions ◽  
Rutile Structure ◽  
The Stability ◽  
The One

<p></p><p>Interfacial metal-oxide systems with ultrathin oxide layers are of high interest for their use in catalysis. In this study, we present a density functional theory (DFT) investigation of the structure of ultrathin rutile layers (one and two TiO<sub>2</sub> layers) supported on TiN and the stability of water on these interfacial structures. The rutile layers are stabilized on the TiN surface through the formation of interfacial Ti–O bonds. Charge transfer from the TiN substrate leads to the formation of reduced Ti<sup>3+</sup> cations in TiO<sub>2.</sub> The structure of the one-layer oxide slab is strongly distorted at the interface, while the thicker TiO<sub>2</sub> layer preserves the rutile structure. The energy cost for the formation of a single O vacancy in the one-layer oxide slab is only 0.5 eV with respect to the ideal interface. For the two-layer oxide slab, the introduction of several vacancies in an already non-stoichiometric system becomes progressively more favourable, which indicates the stability of the highly non-stoichiometric interfaces. Isolated water molecules dissociate when adsorbed at the TiO<sub>2</sub> layers. At higher coverages the preference is for molecular water adsorption. Our ab initio thermodynamics calculations show the fully water covered stoichiometric models as the most stable structure at typical ambient conditions. Interfacial models with multiple vacancies are most stable at low (reducing) oxygen chemical potential values. A water monolayer adsorbs dissociatively on the highly distorted 2-layer TiO<sub>1.75</sub>-TiN interface, where the Ti<sup>3+</sup> states lying above the top of the valence band contribute to a significant reduction of the energy gap compared to the stoichiometric TiO<sub>2</sub>-TiN model. Our results provide a guide for the design of novel interfacial systems containing ultrathin TiO<sub>2</sub> with potential application as photocatalytic water splitting devices.</p><p></p>

Thermodynamic Stability of Hexagonal and Rhombohedral Bn at Cvd Conditions from Van der Waals Corrected First Principles Calculations

2019 ◽  
Author(s):  
Henrik Pedersen ◽  
Björn Alling ◽  
Hans Högberg ◽  
Annop Ektarawong
Keyword(s):  
Thin Films ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Thermal Equilibrium ◽  
Density Functional ◽  
Van Der Waals ◽  
Chemical Vapor ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Stability

Thin films of boron nitride (BN), particularly the sp<sup>2</sup>-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN) are interesting for several electronic applications given band gaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800 K and 1000-10000 Pa, respectively. In this letter, we use van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. We find that r-BN is the stable sp<sup>2</sup>-hybridized phase at CVD conditions, while h-BN is metastable. Thus, our calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

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