Potentials For Transition Metals Research Articles

Transition metal-functionalized porphyrin-like C70 fullerenes as sensors and adsorbents of formaldehyde- DFT, NBO, and QTAIM study

C70 fullerenes are effective formaldehyde sensors and adsorbents, with nitrogen or boron doping significantly increasing their sensitivity in detecting formaldehyde gas. C70 fullerenes doped with nitrogen atoms are effective in removing formaldehyde from the air. In this work, the potential of transition metal- (Ti, Cr, Fe, Ni, and Zn) functionalized porphyrin C70 fullerenes (MF-PC70Fs) for sensing and removing formaldehyde were investigated using DFT, QTAIM, and NBO. The HOMO-LUMO gaps for Ti, Cr, Fe, Ni, and Zn-functionalized materials were computed, resulting in values of 1.27, 0.07, 1.84, 1.84, and 1.80 eV, respectively. The absorption energies of formaldehyde onto MF-PC70Fs were computed, revealing that the PC70Fs functionalized with Ti had the highest adsorption strength, while those functionalized with Ni had the lowest. The HOMO-LUMO gap of Cr- and Fe-functionalized PC70Fs was significantly changed after adsorbing formaldehyde. Accordingly, they may be used as conductivity-type sensors for detecting formaldehyde. Also, Cr-, Fe-, and Zn-functionalized PC70Fs can be used as formaldehyde work function type sensors. According to the calculated time recovery of MF-PC70Fs, Fe- and Zn-functionalized PC70Fs are more favourite materials than Cr-functionalized in formaldehyde sensors.

Relationship between zero-charge potentials, critical passivation potentials, and flat band potentials for transition metals of groups IV–VI of periodic table in neutral alcohol media

The possible relationship between the critical passivation potentials, zero-charge potentials, and flat band potentials for transition metals of groups IV–VI of the periodic table in a series of alcohol solvents; their adsorption on a metal surface results in the transition of the metal into the passive state upon a certain shift in the potential with respect to Eq = 0.

Twenty five years of Finnis–Sinclair potentials

In 1984, the paper, entitled A simple empirical N-body potential for transition metals by M.W. Finnis and J.E. Sinclair appeared in Philosophical Magazine A 1. Twenty five years later, with more th...

Robust quantum-based interatomic potentials for multiscale modeling in transition metals

First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in transition metals and alloys within density-functional quantum mechanics. In the central body-centered cubic (bcc) metals, where multi-ion angular forces are important to materials properties, simplified model GPT (MGPT) potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect, and mechanical properties at both ambient and extreme conditions. Selected applications to multiscale modeling discussed here include dislocation core structure and mobility, atomistically informed dislocation dynamics simulations of plasticity, and thermoelasticity and high-pressure strength modeling. Recent algorithm improvements have provided a more general matrix representation of MGPT beyond canonical bands, allowing improved accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed for dynamic simulations, and the development of temperature-dependent potentials.

AB INITIO DERIVATION OF INTERATOMIC INTERACTIONS IN TRANSITION METALS

An approach to the ab-initio calculation of many-body interatomic potentials in transition metals (TM) is developed. It is based on utilizing the local spin density approximation and linear superposition assumption for the density of the valence electrons. The analytic expressions for the spin dependent pair and triplet interatomic interactions are given. The many-body potentials for three particles and four particles are shown to be indirect and to describe interactions of the same spin orientation.

A theoretical study of the structure and dynamics of amorphous Fe

The extended theory of transition-metal potential, which includes the transition-metal d states, is used to obtain the effective interatomic interactions in terms of pair potential for amorphous Fe. Pair potential for amorphous Fe is also computed using a simple approach for liquid metals given by de-Angelis and March. We employ the so obtained pair potentials to calculate the longitudinal- and transverse-phonon eigenfrequencies using the theory of phonons in amorphous solids. The results for the phonon eigenfrequencies obtained from these potentials are in good qualitative agreement with the molecular-dynamics results as well as with the theoretical results of Bhatia and Singh. Computation of the Debye temperature and the isothermal bulk modulus also shows a close agreement with other results.

Analytic representation of multi-ion interatomic potentials in transition metals.

The first-principles, density-functional version of the generalized pseudopotential theory (GPT), previously developed for empty- and filled-d-band metals, recently has been extended to pure transition metals with partially filled d bands [Phys. Rev. B 38, 3199 (1988)]. Within this formalism, a rigorous real-space expansion of the bulk total energy has been obtained in terms of widely transferable, structure-independent interatomic potentials, including both central-force pair interactions and angular-force triplet and quadruplet interactions. In the central transition metals, the three- and four-ion potentials, ${\mathit{v}}_{3}$ and ${\mathit{v}}_{4}$, are essential to a proper description of materials properties, but are necessarily multidimensional functions which cannot be easily tabulated for application purposes.We develop here a simplified version of the theory, the model GPT, in which these potentials can be expressed analytically while retaining the most important physics of the full first-principles treatment. The analytic treatment of ${\mathit{v}}_{3}$ and ${\mathit{v}}_{4}$ is made possible because of three simplifying features in the central transition metals. First, due to the nonspherical nature of the Fermi surface in such metals, the long-range sp-d hybridization tails of the first-principles potentials destructively interfere in total-energy calculations and thus can be dropped at the outset without major consequences. Second, the direct d-d contributions to the potentials are short ranged and need only be retained to fourth order in interatomic d-state matrix elements to obtain a good representation of the d-band-structure energy. Third, the d bands are canonical in nature, with the interatomic matrix elements well approximated by simple forms, so that all remaining low-order d-state contributions can be evaluated analytically.This leads to a description of ${\mathit{v}}_{3}$ and ${\mathit{v}}_{4}$ in terms of universal short-range radial and angular functions. The model GPT is made quantitatively accurate for real materials by allowing the coefficient of each d-state contribution to be adjusted to match first-principles calculations and/or experimental data. In this manner, one can achieve a set of potentials which simultaneously yield a good description of cohesion, vacancy formation, structural phase stability, elastic constants, and phonons, as is demonstrated for the representative case of molybdenum. More generally, the analytic potentials are suitable for widescale applications and permit for the first time the use of the transition-metal GPT in molecular-dynamics and Monte Carlo simulations.

First-Principles Interatomic Potentials for Transition Metals and Their Surfaces

ABSTRACTFor bulk transition metals, a first-principles generalized pseudopotential theory (GPT) of interatomic potentials has been developed in which the cohesive-energy unctional takes the form of a volume term plus sums over widely transferable two-, three-, and four-ion potentials. The GPT has been further extended to surfaces by making an internal transformation of this functional to an embedded-atom-like format in which the embedding function is identified as the bulk volume term and the atomic volume is replaced by an average electron density. Applications of the bulk and surface GPT to the calculation of structural, vacancy-formation, and surface energies in Cu and Mo, and to the investigation of surface relaxation and reconstruction in Mo are discussed.

A modification of the Finnis-Sinclair potentials for highly deformed and defective transition metals

Abstract A modification is introduced to the original Finnis-Sinclair potentials for transition metals which substantially improves their pressure versus volume behaviour and overcomes their high-compression instability. With this modification good results are obtained for the energetics instability. With this modification good results are obtained for the energetics and the stable configuration of vacancies and interstitials. Excellent agreement is also found between the lattice parameter dependence of the cohesive energy of Mo as obtained using the modified potentials and via self-consistent augmented-spherical-wave calculations. With the proposed modification, the repulsive component of the modified potentials turns out to be akin to a Wedepohl potential.

Self-consistent calculations of rare-gas-transition-metal interaction potentials.

A model Hamiltonian is used to calculate potential-energy surfaces for He and Ne on the (110) faces of Ni, Cu, Pd, and Ag. The calculations are nonperturbative, self-consistent, and contain no parameters which are fittable with respect to the gas-solid interaction. Static image-force effects are included. The theory represents the first quantum-mechanical approach to rare-gas--transition-metal potentials which includes the interaction of the rare-gas orbitals with the d electrons in a consistent way. Corrugation is found to be approximately proportional to the d-electron charge density. The sp band is represented by a Sommerfeld model with hybridization gap, which does not contribute to the corrugation. Part of the potential arises through the hybridization of the rare-gas orbitals with the unoccupied metal states. This interference energy is roughly a factor of 2 larger for neon than for helium, leading to larger corrugations of the neon potentials as compared with the helium potentials. This is in agreement with recent experiments, but in contrast to earlier theoretical predictions. The theoretically calculated corrugations and well depths compare reasonably to the experimental data where available. The computed values of corrugation for He increase in the order Ni, Cu, Ag, and Pd. This agrees with experiments where soft potentials have been fitted to the scattering data, although the predicted He/Ni(110) corrugation is overly large by more than a factor of 2. With increasing energy, the He corrugation increases slightly in the calculations. The dependence is nearly constant for Ni and strongest for Pd. For Ne/Ni(110) and Ne/Pd(110) corrugation decreases with energy. Image-force effects are found to be important for the corrugation and softness of the neon potentials.

First-principles interatomic potentials in transition metals.

The first ab initio theory of structure-independent interatomic potentials in $d$-electron transition metals has been developed from a multi-ion expansion of the total energy within the density-functional formalism. Explicit results for the volume term and two-ion and three-ion potentials entering this expansion have been obtained and successfully tested for $3d$-series metals.

Correlation effects in ferromagnetism of transition metals

The effect of electronic correlations on the ferromagnetic instabilities, effective local moments, and fluctuations in spin and charge in a transition metal is discussed with a model Hamiltonian which includes intraatomic Coulomb and exchange interactions. The one-particle properties of $d$ electrons are described by bcc and fcc canonical bands. We find that reduction of density fluctuations and formation of local moments change the Stoner criterion and the condition for the ground state to be completely ferromagnetic. The magnetic states of Fe, Co, and Ni are studied in more detail, where the electrons are found to be considerably correlated for realistic model parameters. Redistribution of electrons between the ${e}_{g}$ and ${t}_{2g}$ states seen there causes deviations from the Stoner theory and is responsible for different exchange splittings of both types of states. The results are in qualitative agreement with the experimental data and suggest the use of anisotropic exchange correlation potentials in transition metals.

Analytical properties of theS-matrix applied to the resonance model of transition metals

A method to construct ionic potentials for transition metals from the knowledge of the resonantd-band phase shiftη2=tg-21/2W/(E-Ed) is developed. This is based on an inversescattering approach using the analytic properties of theS-matrix and Jost functions to reconstruct the interparticle potential in the spirit of the Marchenko and Gel'fand-Levitan formalisms. A specific form of the solution of the resulting integral equation is discussed and possible applications to a host of transition metal properties are outlined.

Variational treatment of electronic correlations ind-band metals

We discuss the effects of electronic correlation on the ground state energy, effective local moment and charge fluctuations for a model of transition metals. The model consists of a bcc or fcc-canonicald-band with intraatomic Coulomb and exchange interaction. We find that for realistic interaction parameters the correlated state shows enhanced spinfluctuations indicating the formation of local moments and strongly reduced charge fluctuations compared to the HF state. We also find that in generale g andt 2g -states can show a different extent of correlation which suggests the use of anisotropic exchange correlation potentials in transition metals. The application of our model to bcc iron and fcc nickel is also considered.

Interatomic potentials in transition metals

Abstract The different roles played by the valence s and d electrons in determining the bulk properties of pure transition metals is described. In the light of this the expected behaviour of the inert gas-metal and metal-metal interatomic potentials is discussed.