Diffusion of ferrocene through vanadyl phosphate by density functional theory.

Here, we employed the nudged elastic band (NEB) method to simulate the diffusion of ferrocene through vanadyl phosphate (VOPO), with a focus on understanding the diffusion pathways arising from the complex structure of ferrocene. We systematically evaluated a total of 36 potential diffusion paths, categorizing them into three groups based on their directional orientation: 15 paths between V sites along the [110] direction, 15 paths from V to P sites along the [100] direction, and 6 paths between P sites also along the [110] direction. Our analysis revealed that the energy barriers for diffusion along the [110] direction typically ranged between 0.

Incorporating solvent effects in DFT: insights from cation exchange in faujasites.

Zeolites are versatile materials renowned for their extra-framework cation exchange capabilities, with applications spanning diverse fields, including nuclear waste treatment. While detailed experimental characterization offers valuable insight, density functional theory (DFT) proves particularly adept at investigating ion exchange in zeolites, owing to its atomic and electronic resolution. However, the prevalent occurrence of zeolitic ion exchange in aqueous environments poses a challenge to conventional DFT modeling, traditionally conducted in a vacuum.

Friends or Foes: Fundamental Principles of Th-Organic Scaffold Chemistry Using Zr-Analogs as a Guide.

The fundamental interest in actinide chemistry, particularly for the development of thorium-based materials, is experiencing a renaissance owing to the recent and rapidly growing attention to fuel cycle reactors, radiological daughters for nuclear medicine, and efficient nuclear stockpile development. Herein, we uncover fundamental principles of thorium chemistry on the example of Th-based extended structures such as metal-organic frameworks in comparison with the discrete systems and zirconium extended analogs, demonstrating remarkable over two-and-half-year chemical stability of Th-based frameworks as a function of metal node connectivity, amount of defects, and conformational linker rigidity through comprehensive spectroscopic and crystallographic analysis as well as theoretical modeling. Despite exceptional chemical stability, we report the first example of studies focusing on the reactivity of the most chemically stable Th-based frameworks in comparison with the discrete Th-based systems such as metal-organic complexes and a cage, contrasting multicycle recyclability and selectivity (>97%) of the extended structures in comparison with the molecular compounds.

Bioconjugation of COL1 protein on liquid-like solid surfaces to study tumor invasion dynamics.

Tumor invasion is likely driven by the product of intrinsic and extrinsic stresses, reduced intercellular adhesion, and reciprocal interactions between the cancer cells and the extracellular matrix (ECM). The ECM is a dynamic material system that is continuously evolving with the tumor microenvironment. Although it is widely reported that cancer cells degrade the ECM to create paths for migration using membrane-bound and soluble enzymes, other nonenzymatic mechanisms of invasion are less studied and not clearly understood.

Capture Instead of Release: Defect-Modulated Radionuclide Leaching Kinetics in Metal-Organic Frameworks.

Comparison of defect-controlled leaching-kinetics modulation of metal-organic frameworks (MOFs) and porous functionalized silica-based materials was performed on the example of a radionuclide and radionuclide surrogate for the first time, revealing an unprecedented readsorption phenomenon. On a series of zirconium-based MOFs as model systems, we demonstrated the ability to capture and retain >99% of the transuranic Am radionuclide after 1 week of storage. We report the possibility of tailoring radionuclide release kinetics in MOFs through framework defects as a function of postsynthetically installed organic ligands including cation-chelating crown ether-based linkers.

Heterometallic multinuclear nodes directing MOF electronic behavior.

Metal node engineering in combination with modularity, topological diversity, and porosity of metal-organic frameworks (MOFs) could advance energy and optoelectronic sectors. In this study, we focus on MOFs with multinuclear heterometallic nodes for establishing metal-property trends, , connecting atomic scale changes with macroscopic material properties by utilization of inductively coupled plasma mass spectrometry, conductivity measurements, X-ray photoelectron and diffuse reflectance spectroscopies, and density functional theory calculations. The results of Bader charge analysis and studies employing the Voronoi-Dirichlet partition of crystal structures are also presented.

Heterometallic Actinide-Containing Photoresponsive Metal-Organic Frameworks: Dynamic and Static Tuning of Electronic Properties.

Acquiring fundamental knowledge of properties of actinide-based materials is a necessary step to create new possibilities for addressing the current challenges in the nuclear energy and nuclear waste sectors. In this report, we established a photophysics-electronics correlation for actinide-containing metal-organic frameworks (An-MOFs) as a function of excitation wavelength, for the first time. A stepwise approach for dynamically modulating electronic properties was applied for the first time towards actinide-based heterometallic MOFs through integration of photochromic linkers.

Thermodynamics and Electronic Properties of Heterometallic Multinuclear Actinide-Containing Metal-Organic Frameworks with "Structural Memory".

Thermodynamic studies of actinide-containing metal-organic frameworks (An-MOFs), reported herein for the first time, are a step toward addressing challenges related to effective nuclear waste administration. In addition to An-MOF thermochemistry, enthalpies of formation were determined for the organic linkers, 2,2'-dimethylbiphenyl-4,4'-dicarboxylic acid (HMeBPDC) and biphenyl-4,4'-dicarboxylic acid (HBPDC), which are commonly used building blocks for MOF preparation. The electronic structure of the first example of An-MOF with mixed-metal AnAn'-nodes was influenced through coordination of transition metals as shown by the density of states near the Fermi edge, changes in the Tauc plot, conductivity measurements, and theoretical calculations.

Galvanic Replacement-Driven Transformations of Atomically Intermixed Bimetallic Colloidal Nanocrystals: Effects of Compositional Stoichiometry and Structural Ordering.

Galvanic replacement reactions dictated by deliberately designed nanoparticulate templates have emerged as a robust and versatile approach that controllably transforms solid monometallic nanocrystals into a diverse set of architecturally more sophisticated multimetallic hollow nanostructures. The galvanic atomic exchange at the nanoparticle/liquid interfaces induces a series of intriguing structure-transforming processes that interplay over multiple time and length scales. Using colloidal Au-Cu alloy and intermetallic nanoparticles as structurally and compositionally fine-tunable bimetallic sacrificial templates, we show that atomically intermixed bimetallic nanocrystals undergo galvanic replacement-driven structural transformations remarkably more complicated than those of their monometallic counterparts.

Graphene-Titanium Interfaces from Molecular Dynamics Simulations.

Unraveling the physical and chemical properties of graphene-metal contacts is a key step toward the development of graphitic electronic nanodevices. Although many studies have revealed the way that various metals interact with graphene, few have described the structure and behavior of large pieces of graphene-metal nanostructures under different conditions. Here, we present the first classical molecular dynamics study of graphene-titanium (G-Ti) structures, with and without substrates.

First-principles investigation of intrinsic defects and self-diffusion in ordered phases of VC.

The self-diffusion behavior of vanadium subcarbide (VC) is investigated using density functional theory calculations, owing to its potential application as a diffusion barrier in nuclear applications. Three ordered VC structures, two of which correspond to experimentally observed phases, are characterized in terms of their equilibrium structural, electronic and elastic properties. Our model for self-diffusion in VC considers diffusion of carbon and vanadium to occur separately on each sublattice.

Charge optimized many body (COMB) potentials for Pt and Au.

Interatomic potentials for Pt and Au are developed within the third generation charge optimized many-body (COMB3) formalism. The potentials are capable of reproducing phase order, lattice constants, and elastic constants of Pt and Au systems as experimentally measured or calculated by density functional theory. We also fit defect formation energies, surface energies and stacking fault energies for Pt and Au metals.

Effect of Surface Chemistry on Water Interaction with Cu(111).

The interfacial dynamics of water in contact with bare, oxidized, and hydroxylated copper surfaces are examined using classical molecular dynamics (MD) simulations. A third-generation charge-optimized many-body (COMB3) potential is used in the MD simulations to investigate the adsorption of water molecules on Cu(111), and the results are compared to the findings of density functional theory (DFT) calculations. The adsorption energies and structures predicted by COMB3 are generally consistent with those determined with DFT.

First-principles investigation of ferroelectricity in LaBGeO5.

Density functional theory calculations are performed to characterize the structural, electronic and vibrational properties of both the low-temperature ferroelectric and high-temperature paraelectric phases of LaBGeO5. Phonon dispersion calculations for the high-temperature phase reveal an unstable mode whose zone-center eigenvector corresponds to a rigid rotation of the BO4 tetrahedra, in agreement with previous calculations based on a short-range model potential. A possible switching path between two symmetry-equivalent ferroelectric phases that goes through the high-temperature paraelectric phase is identified and used to calculate the spontaneous polarization.

Charge optimized many-body (COMB) potential for dynamical simulation of Ni-Al phases.

An interatomic potential for the Ni-Al system is presented within the third-generation charge optimized many-body (COMB3) formalism. The potential has been optimized for Ni3Al, or the γ' phase in Ni-based superalloys. The formation energies predicted for other Ni-Al phases are in reasonable agreement with first-principles results.

Charge optimized many-body (COMB) potential for Al2O3 materials, interfaces, and nanostructures.

This work presents the development and applications of a new empirical, variable charge potential for Al2O3 systems within the charge optimized many-body (COMB) potential framework. The potential can describe the fundamental physical properties of Al2O3, including cohesive energy, elastic constants, defect formation energies, surface energies and phonon properties of α-Al2O3 comparable to that obtained from experiments and first-principles calculations. The potential is further employed in classical molecular dynamics (MD) simulations to validate and predict the properties of the Al (1 1 1)-Al2O3 (0 0 0 1) interface, tensile properties of Al nanowires, Al2O3 nanowires, Al2O3-covered Al nanowires, and defective Al2O3 nanowires.

Charge optimized many-body potential for aluminum.

An interatomic potential for Al is developed within the third generation of the charge optimized many-body (COMB3) formalism. The database used for the parameterization of the potential consists of experimental data and the results of first-principles and quantum chemical calculations. The potential exhibits reasonable agreement with cohesive energy, lattice parameters, elastic constants, bulk and shear modulus, surface energies, stacking fault energies, point defect formation energies, and the phase order of metallic Al from experiments and density functional theory.

A charge optimized many-body (COMB) potential for titanium and titania.

This work proposes an empirical, variable charge potential for Ti and TiO(2) systems based on the charge-optimized many-body (COMB) potential framework. The parameters of the potential function are fit to the structural and mechanical properties of the Ti hcp phase, the TiO(2) rutile phase, and the energetics of polymorphs of both Ti and TiO(2). The relative stabilities of TiO(2) rutile surfaces are predicted and compared to the results of density functional theory (DFT) and empirical potential calculations.

A charge optimized many-body potential for titanium nitride (TiN).

This work presents a new empirical, variable charge potential for TiN systems in the charge-optimized many-body potential framework. The potential parameters were determined by fitting them to experimental data for the enthalpy of formation, lattice parameters, and elastic constants of rocksalt structured TiN. The potential does a good job of describing the fundamental physical properties (defect formation and surface energies) of TiN relative to the predictions of first-principles calculations.

A charge-optimized many-body potential for the U-UO2-O2 system.

Building on previous charge-optimized many-body (COMB) potentials for metallic α-U and gaseous O2, we have developed a new potential for UO2, which also allows the simulation of U-UO2-O2 systems. The UO2 lattice parameter, elastic constants and formation energies of stoichiometric and non-stoichiometric intrinsic defects are well reproduced. Moreover, this is the first rigid-ion potential that produces the correct deviation of the Cauchy relation, as well as the first classical interatomic potential that is able to determine the defect energies of non-stoichiometric intrinsic point defects in UO2 with an appropriate reference state.

Phonon lifetime investigation of anharmonicity and thermal conductivity of UO2 by neutron scattering and theory.

Inelastic neutron scattering measurements of individual phonon lifetimes and dispersion at 295 and 1200 K have been used to probe anharmonicity and thermal conductivity in UO2. They show that longitudinal optic phonon modes carry the largest amount of heat, in contrast to past simulations and that the total conductivity demonstrates a quantitative correspondence between microscopic and macroscopic phonon physics. We have further performed first-principles simulations for UO2 showing semiquantitative agreement with phonon lifetimes at 295 K, but larger anharmonicity than measured at 1200 K.

Variable charge reactive potential for hydrocarbons to simulate organic-copper interactions.

A variable charge reactive empirical potential for carbon-based materials, hydrocarbons, organometallics, and their interfaces is developed within the framework of charge optimized many-body (COMB) potentials. The resulting potential contains improved expressions for the bond order and self-energy, which gives a flexible, robust, and integrated treatment of different bond types in multicomponent and multifunctional systems. It furthermore captures the dissociation and formation of the chemical bonds and appropriately and dynamically determines the associated charge transfer, thus providing a powerful method to simulate the complex chemistry of many-atom systems in changing environments.

Classical interatomic potential for orthorhombic uranium.

A classical interatomic potential for uranium metal is derived within the framework of the charge optimized many body (COMB) formalism. The potential is fitted with a database obtained from experiment and density functional theory (DFT) calculations. The potential correctly predicts orthorhombic α-U to be the ground state.

Effect of fluorocarbon molecules confined between sliding self-mated PTFE surfaces.

We report on the frictional response and atomic process that occur when molecular fluorocarbon molecules of varying lengths are sheared between two polytetrafluoroethylene (PTFE) surfaces. The thicknesses of the molecular layers are also varied. The approach is classical molecular dynamics simulations using a reactive bond-order potential parametrized for fluorocarbons.