Equilibrium Interatomic Distances Research Articles

Innovative thermal process for high-purity group IV metal synthesis: Insights via DFT and MD simulations

The synthesis of group IV transition metals (TMs) such as Ti, Zr, and Hf from their respective oxides (TMO2) poses significant challenges with current methods. There is an urgent need for an environmentally friendly and versatile approach to establish sustainable, efficient, and adaptable TM synthesis technology from TMO2. In this study, the LN process (Lee-Nersisyan), a novel and straightforward approach that employs CaMg2 as the reductant for TMO2 powders is introduced. This innovative strategy involves the thermal processing of TMO2+kCaMg2 mixtures (with k values ranging from 2 to 5 moles) in an argon atmosphere at temperatures between 800 and 1200 °C. The process yields high-purity TM powder with particle sizes in the range of 5–25 μm and oxygen content of less than 0.2 wt%. We apply density-functional theory (DFT) to elucidate the interaction energies and equilibrium interatomic distances between Ti-Ca, Ti-Mg, Ca-Mg, Mg-Mg, Ca-Ca, and Ti-Ti metallic pairs. Additionally, we discuss the growth behavior of TM particles through molecular dynamics simulation (MD) employing LAMMPS. Our LN process represents a promising solution for efficient and sustainable TM synthesis from TMO2.

Effects of nonlinearity and a new nonlinear resonance in two-path phonon transmittance in lattices with two-dimensional arrays of atomic defects.

The paper is devoted to analytical and numerical studies of the effects of nonlinearity on the two-path phonon interference in the transmission through two-dimensional arrays of atomic defects embedded in a lattice. The emergence of transmission antiresonance (transmission node) in the two-path system is demonstrated for the few-particle nanostructures, which allow us to model both linear and nonlinear phonon transmission antiresonances. The universality of destructive-interference origin of transmission antiresonances of waves of different nature, such as phonons, photons, and electrons, in two-path nanostructures and metamaterials is emphasized. Generation of the higher harmonics as a result of the interaction of lattice waves with nonlinear two-path atomic defects is considered, and the full system of nonlinear algebraic equationsis obtained to describe the transmission through nonlinear two-path atomic defects with an account for the generation of second and third harmonics. Expressions for the coefficients of lattice energy transmission through and reflection from the embedded nonlinear atomic systems are derived. It is shown that the quartic interatomic nonlinearity shifts the antiresonance frequency in the direction determined by the sign of the nonlinear coefficient and enhances in general the transmission of high-frequency phonons due to third harmonic generation and propagation. The effects of the quartic nonlinearity on phonon transmission are described for the two-path atomic defects with a different topology. Transmission through the nonlinear two-path atomic defects is also modeled with the simulation of the phonon wave packet, for which the proper amplitude normalization is proposed and implemented. It is shown that the cubic interatomic nonlinearity red shifts in general the antiresonance frequency for longitudinal phonons independently of the sign of the nonlinear coefficient, and the equilibrium interatomic distances (bond lengths) in the atomic defects are changed by the incident phonon due to cubic interatomic nonlinearity. For longitudinal phonons incident on a system with the cubic nonlinearity, the new narrow transmission resonance on the background of a broad antiresonance is predicted to emerge, which we relate to the opening of the additional transmission channel for the phonon second harmonic through the nonlinear defect atoms. Conditions of the existence of the new nonlinear transmission resonance are determined and demonstrated for different two-path nonlinear atomic defects. A two-dimensional array of embedded three-path defects with an additional weak transmission channel, in which a linear analog of the nonlinear narrow transmission resonance on the background of a broad antiresonance is realized, is proposed and modeled. The presented results provide better understanding and detailed description of the interplay between the interference and nonlinearity in phonon propagation through and scattering in two-dimensional arrays of two-path anharmonic atomic defects with a different topology.

The three-center two-positron bond.

Computational studies have shown that one or more positrons can stabilize two repelling atomic anions through the formation of two-center positronic bonds. In the present work, we study the energetic stability of a system containing two positrons and three hydride anions, namely 2e+[H3 3-]. To this aim, we performed a preliminary scan of the potential energy surface of the system with both electrons and positrons in a spin singlet state, with a multi-component MP2 method, that was further refined with variational and diffusion Monte Carlo calculations, and confirmed an equilibrium geometry with D 3h symmetry. The local stability of 2e+[H3 3-] is demonstrated by analyzing the vertical detachment and adiabatic energy dissociation channels. Bonding properties of the positronic compound, such as the equilibrium interatomic distances, force constants, dissociation energies, and bonding densities are compared with those of the purely electronic H3 + and Li3 + systems. Through this analysis, we find compelling similarities between the 2e+[H3 3-] compound and the trilithium cation. Our results strongly point out the formation of a non-electronic three-center two-positron bond, analogous to the well-known three-center two-electron counterparts, which is fundamentally distinct from the two-center two-positron bond [D. Bressanini, J. Chem. Phys., 2021, 155, 054306], thus extending the concept of positron bonded molecules.

Validation of a constrained 2D slab model for water adsorption simulation on 1D periodic TiO2 nanotubes

Solar light driven hydrogen evolution is one focus of modern materials research. Among the different emerging technologies, particular interest is devoted towards metal oxide photocatalysts in the form of various 1D nanostructures. Presently, the mismatch between regular structures that can be synthesized and the largest structures that are feasible for computer simulation is still very large. For example, an in-depth study of water adsorption on nanotube (NT) surfaces requires, in addition to DFT calculations, molecular dynamics simulations to take into account the disordered nature of the aqueous phase. To completely immerse even a very thin nanotube into an aqueous system requires very large system sizes, the modeling of which is computationally extremely expensive. On the other hand, the typical surface science approach when modeling planar interfaces is computationally much less demanding, but can be adequate only for NTs of very large diameters possessing low strain energies. Here, we present three simplified slab models derived from local NT geometries as approximations for inner and outer interfaces of thin TiO2 NTs. In order to describe the role of NT strain on the electronic structure of the water/NT interface, these models contain additional constraints on some of the atoms to alleviate some of the shortcomings of the slab approach. We use the energy of water adsorption, equilibrium interatomic distances, calculated densities of states (DOS) and Mulliken charge distribution as criteria for estimating the model quality. Specifically we analyze the suitability of this approach for the very thin TiO2 (001) slab and the thicker TiO2 (001) NT.

New Orbital Free Simulation Method Based on the Density Functional Theory

A practical way to simulate multi-atomic systems without using of wave functions (orbitals) is proposed. Kinetic functionals for each type of atoms are constructed and then are used for complex systems. On examples of clusters containing Al, Si, C, and O it is shown that this method can describe structures and energies of multi-atomic systems not worse than the Kohn-Sham method but faster. Besides, it is demonstrated that the orbital-free version of the density functional theory may be used for finding equilibrium configurations of multi-atomic systems with covalent bonding. The equilibrium interatomic distances, interbonding angles and binding energies for Si3 and C3 clusters are found in good accordance with known data.

Development of the Orbital-Free Density Functional Approach: The Problem of Angles between Covalent Bonds

The Paulie’s principle is used for development of the orbital-free (OF) version of the density functional theory. On the example of the three-atomic clusters, Al3, Si3, and C3, it is shown that the OF approach may lead to equilibrium configurations of atomic systems with both the metallic and covalent bonding. The equilibrium interatomic distances, interbonding angles and binding energies are found in good accordance with the known data. Results will be useful for developing of theoretical study of huge molecules and nanoparticles.

Modulating Strain and Charge Transfers in Low Dimensional Catalysts through Interface Design and Templated Growth

In this presentation, we review the dimensional aspects of structure-driven surface properties of metal monolayers grown on a Au and graphene/Au templates. Here, surface limited electrodeposition is used to provide precise layer-by-layer growth of Pt monolayers. After a few iterations of SLRR, we find that fully wetted 4-5 monolayer Pt films can be grown on either template. Incorporating graphene at the Pt-Au interface modifies the growth mechanism, charge transfers, equilibrium interatomic distances and associated strain of the synthesized Pt monolayers. Capping the Pt with a single overlayer of graphene similarly affects the underlying Pt structures. X-ray photoelectron spectroscopy (XPS) and extended x-ray absorption fine structure (EXAFS) techniques are used to examine charge mediation across Pt-Graphene-Au junction and the local atomic arrangement as a function of the Pt adlayer dimension. Cyclic voltammetry (CV) and the oxygen reduction reaction (ORR) are used as probes to examine the electrochemically active area of Pt monolayers and catalyst activity, respectively. Results show that the inserted graphene monolayer results in increased activity for the Pt due to a graphene-induced compressive strain, as well as a higher retention of catalytically active Pt surface. This Pt retention extremely effective, and occurs with no compromise to ORR activity, when the Pt is capped with a graphene layer.

Layer-by-layer evolution of structure, strain, and activity for the oxygen evolution reaction in graphene-templated Pt monolayers.

In this study, we explore the dimensional aspect of structure-driven surface properties of metal monolayers grown on a graphene/Au template. Here, surface limited redox replacement (SLRR) is used to provide precise layer-by-layer growth of Pt monolayers on graphene. We find that after a few iterations of SLRR, fully wetted 4-5 monolayer Pt films can be grown on graphene. Incorporating graphene at the Pt-Au interface modifies the growth mechanism, charge transfers, equilibrium interatomic distances, and associated strain of the synthesized Pt monolayers. We find that a single layer of sandwiched graphene is able to induce a 3.5% compressive strain on the Pt adlayer grown on it, and as a result, catalytic activity is increased due to a greater areal density of the Pt layers beyond face-centered-cubic close packing. At the same time, the sandwiched graphene does not obstruct vicinity effects of near-surface electron exchange between the substrate Au and adlayers Pt. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) techniques are used to examine charge mediation across the Pt-graphene-Au junction and the local atomic arrangement as a function of the Pt adlayer dimension. Cyclic voltammetry (CV) and the oxygen reduction reaction (ORR) are used as probes to examine the electrochemically active area of Pt monolayers and catalyst activity, respectively. Results show that the inserted graphene monolayer results in increased activity for the Pt due to a graphene-induced compressive strain, as well as a higher resistance against loss of the catalytically active Pt surface.

Quantum-mechanical modeling without wave functions

It has been shown that the variational principle can be used as the practical way to find the electron density and the total energy in terms of the density functional theory without solving the Kohn-Sham equations (the so-called orbital-free approach). The equilibrium interatomic distances and binding energies found using examples of diatomic systems Si2, Al2, and P2 are in good agreement with the published data. The results obtained for Si-Al, Si-P, and Al-P dimers are also close to the results obtained by the Kohn-Sham method.

A Practical Way to Develop the Orbital-free Density Functional Calculations

Aims: For modeling of large polyatomic systems one may use the variation principle for energy density functional. The key point to make this is to find the functional of kinetic energy in the orbital -freeapproach. Study Design:We describe a way to find functionals of kinetic energy for single atoms and to use them for modeling of polyatomic systems. On examples of diatomic systems Si2, Al2, and P2the equilibrium interatomic distances and binding energies were calculated in good comparison with published data. Results for Si -Al, Si-P and Al-P dimers are also close to results of Kohn -Sham calculations. Place and Duration of Study:Institute of Materials, Khabarovsk, Russia ; Institute of Applied Mathematics,Khabarovsk, Russia;2011-2013. Methodology: We worked in the frameworks of pseudo potentials and the local density approximation of the density functional theory. We used the Kohn -Sham calculations as

A Simple Quantum Mechanics Way to Simulate Nanoparticles and Nanosystems without Calculation of Wave Functions

It is shown that the variation principle can be used as a practical way to find the electron density and the total energy in the frame of the density functional theory (DFT) without solving of the Kohn-Sham equation. On examples of diatomic systems Si2, Al2, and N2, the equilibrium interatomic distances and binding energies have been calculated in good comparison with published data. The method can be improved to simulate nanoparticles containing thousands and millions atoms.

How large are the microscopic electronic dipole (hyper)polarizabilities of Cd nTe n bare clusters compared to those of Cd nS n and Cd nSe n? A systematic ab initio study

The static mean dipole polarizabilities, the polarizability anisotropies and the second hyperpolarizabilities of the ground state structures of stoichiometric Cd n Te n ( n = 2, 3, 4, 5, 9) clusters are presented for the first time and they are compared with those of selected Cd n S n and Cd n Se n clusters. Our ab initio results suggest that the CdTe clusters are significantly more hyperpolarizable than clusters constituted by CdS, and CdSe, in accordance to earlier experimental measurements. Also, it is demonstrated that the second hyperpolarizability magnitudes computed at different theoretical equilibrium geometries of the same cluster, determined by geometry optimization at different levels of theory, are significantly sensitive to the obtained equilibrium inter-atomic distances among the electropositive Cd atoms.

Computational studies of CO and CO +: Density functional theory and time-dependent density functional theory

Potential energy curves, equilibrium interatomic distances, term energies and harmonic vibration frequencies for the 16 lowest states of neutral carbon monoxide and the six lowest states of singly ionized carbon monoxide are calculated by density functional theory (DFT) and linear-response time-dependent density functional (LR-TDDFT) theory. The results are compared with experimental data. The two theories, DFT and LR-TDDFT, are described briefly.

MRCI potential curves and analytical potential energy functions of the low-lying excited states (1∏，3∏) of ZnHg

The multireference configuration interaction (MRCI) electronic energy calculations with effective core potentials have been carried out for two low-lying excited states (1∏,3∏) of ZnHg dimer. Potential energy curves (PECs) are generated. The PECs are fitted to analytical potential energy functions (APEFs) using the Murrel-Sorbie potential function. The computational equilibrium interatomic distances and dissociation energies are compared with the theoretical values available in the literature. Some important spectroscopic parameters are calculated. Based on the PECs, the vibrational levels of the two states are predicted by solving Schrdinger equation of nuclear motion.

Ab initio calculations of accurate dissociation energy and analytic potential energy function for the second excited state B 1 Π of 7 LiH

The reasonable dissociation limit of the second excited singlet state B1Π of 7LiH molecule is obtained. The accurate dissociation energy and equilibrium geometry of the B1Π state are calculated using a symmetry-adapted-cluster configuration–interaction method in full active space. The whole potential energy curve for the B1Π state is obtained over the internuclear distance ranging from about 0.10 nm to 0.54 nm, and has a least-square fit to the analytic Murrell–Sorbie function form. The vertical excitation energy is calculated from the ground state to the B1Π state and compared with previous theoretical results. The equilibrium internuclear distance obtained by geometry optimization is found to be quite different from that obtained by single-point energy scanning under the same calculation condition. Based on the analytic potential energy function, the harmonic frequency value of the B1Π state is estimated. A comparison of the theoretical calculations of dissociation energies, equilibrium interatomic distances and the analytic potential energy function with those obtained by previous theoretical results clearly shows that the present work is more comprehensive and in better agreement with experiments than previous theories, thus it is an improvement on previous theories.

Molecular Dynamics Study of Icosahedral Clusters in Ni–ZrAmorphous Alloys

Formation of icosahedral clusters in rapidly solidified binaryamorphous NixZr100−x (x = 15, 33.3, 50, 66.7, 85) isstudied by using molecular dynamics simulation methods. A large numberof icosahedral clusters with 13 atoms (Ih13) were observed inNixZr100−x alloys, and most of them, even those inZr-rich alloys, are found to be Ni-centred. Studies on the structuresof Ni33.3Zr66.7 obtained at different cooling ratesdemonstrate that most of iscosahedral clusters enhanced by decreasingcooling rates are also Ni-centred. The essentials of Ni atomspreferring to be the core of icosahedral clusters are illustrated withthe criterion of energy minimization and the equilibrium interatomicdistances between different atoms.

Ab initio calculation on the analytic potential energy functions for the state a 3 Σ + u and the state b 3 Π u of spin-aligned trimer 7 Li 2

The energies, equilibrium geometries and harmonic frequencies of the triplet excited states (a3Σu+ and b3Πu) of spin-aligned trimer 7Li2 are firstly calculated by using a symmetry adapted cluster-configuration interaction method. The potential curves for the two excited states have least squares fitted by the Murrell–Sorbie function. The spectroscopic data (Be, αe, ωe and ωe χe) and the force constants (f2, f3 and f4) are calculated. It is found that the spin-aligned triplet excited state b3Πu is more stable than the ground state X1Σg+ and that the Murrell–Sorbie function form is suitable not only for the ground state but also for the spin-aligned triplet excited states. Comparison between the theoretical determinations of dissociation energies, equilibrium interatomic distances and harmonic frequencies with the experimental data about a3Σu+ and b3Πu clearly shows that the present work represents a significant improvement in agreement between theories and experiments.

Correlation of magnetic transition temperatures to disorder for atomically arranged perovskites

Oxygen contents and the A–O and Mn–O bond lengths have been measured over extended temperature and composition ranges to derive accurate equilibrium interatomic distances for perovskite manganites AMnO 3. By using these parameters instead of tabulated ionic radii we have derived the functional dependence of the tolerance factor t= t( x, T, δ) on composition, temperature, and oxygen content. This functional dependence of t= t( x, T, δ) permits a systematic representation of perovskite phase stability, structural distortions, and magnetic transition temperatures in terms of the tolerance factor. An additional dependence of the properties on local structural and charge disorder on the A-site is demonstrated for the Sr 1− x Ca x MnO 3 and RE 0.5Ba 0.5MnO 3 compounds. These effects also appear to be universal for other perovskites-like compounds; for example, the high temperature superconducting cuprates.

A variety of metal chalcogenide clusters: MOLCAO calculations and interplay between quantum-sized semiconductors and multinuclear complexes

Abstract Several series of metal chalcogenide clusters as examples of cadmium sulfide composition are considered. They are distinguished in the geometrical construction rules and cover a large variety of Cd x S y structures known from experimental data on the ligand-capped cadmium sulfide clusters and some new structures. On the basis of ab initio quantum chemical calculations with RHF MOLCAO method properties of Cd x S y ( x ≤17, y ≤28) clusters are analysed with and without termination at sulfur dangling bonds. Changes of equilibrium interatomic distances, effective charges and energetic characteristics are shown within the cluster series depending on number of atoms and type of termination.

Adhesion of metal on metal. The Pt on Co case

The adhesion of Pt overlayers in pseudomorphic epitaxy on hcp Co(0 0 0 1) and fcc Co(1 0 0) was investigated with first-principles calculations. This was compared to the adhesion of the Pt surface layers on Pt(1 1 1) and Pt(1 0 0). We show that adhesion can be analyzed by taking into account the interplay between the chemical and structural properties at the interface. The free Pt planes with the bulk Pt–Pt distance are submitted to tensile stress which can be relaxed by 6.6% and 9.1% contraction for the (1 1 1) and (1 0 0) symmetries respectively. This results in equilibrium interatomic distances which are not far from that of the Co substrate. Consequently the stress energy in a pseudomorphic Pt monolayer on a Co substrate is lower than the stress energy of pure Pt(1 1 1) or Pt(1 0 0) surfaces. However, this is at the expense of the Pt chemical reactivity towards the Co substrate. This is in agreement with the general dependence between chemical reactivity and stress of a metal surface.