Atomic Cohesive Energy Research Articles

Influences of size, shape, and wall thickness on melting entropy and enthalpy of metallic nanostructures

From the perspective of a bond-order-length-strength correlation, we put forward an analytical solution to describe the size, shape, and wall thickness dependency of melting temperature, entropy, and enthalpy for metallic nanostructures. Theoretical reproduction of measurements clarified that (i) when the crystal size reduces, the atomic coordination number lowers, the atomic cohesive energy decreases, and the surface-to-volume ratio increases; (ii) at the same equivalent radius, with the decrease in the number of sides for polyhedral nanoparticles and polygonal nanowires or nanotubes, the melting temperature, entropy, and enthalpy depress; and (iii) the melting temperature, entropy, and enthalpy of nanotubes are always lower than those of nanowires with the same cross-sectional radius. The present formulation is accurate and convenient, which not only shows deeper insight into the physical origins of a melting thermodynamic property response to perturbations but also provides guidance for the design and optimization of electronic nanodevices.

Multifield driven bond relaxation on the dielectric constant of GaN, InN, and ZnO

From the perspective of bond relaxation under multifield perturbation, we examined the dielectric response to perturbation for GaN, InN, and ZnO. It is found that the surface local bond contraction and quantum entrapment dictate the size dependency of the dielectric constant at the nanometer scale. Reproduction of experimental observations under temperature, pressure, and tensile strain derived respective information of the Debye temperature and atomic cohesive energy, the bulk modulus and energy density, the bond length, bond energy, and force constant. The formulation of the multifield effects on the dielectric constant of semiconductors is beyond the scope of the available approaches, which not only revealed quantitative information but also provides deeper insight into the physical origin of the dielectric response to perturbations.

Determination of the atomic cohesive energy and Debye temperature from thermal stiffening of the dielectric constant of semiconductors

From the perspective of bond-order-length-strength correlation, we have formulated the thermally stiffened dielectric constant and refractive index for semiconductors. It is clarified that: (i) The dielectric constant and refractive index of semiconductors turn from non-linear to linear thermal stiffening at one third of its Debye temperature; (ⅱ) The Debye temperature determines the width of the non-linear part and the reciprocal atomic cohesive energy determines the slope of linear part at high temperatures of the dielectric constant and refractive index curves.

Frank-van der Merwe growth in bilayer graphene

Frank-van der Merwe growth in bilayer graphene

Surface, size and thermal effects in alkali metal with core-electron binding-energy shifts

Consistency between density functional theory calculations and X-ray photoelectron spectroscopy measurements confirms our predications on the undercoordination-induced local bond relaxation and core level shift of alkali metal, which determine the surface, size and thermal properties of materials. Zone-resolved photoelectron spectroscopy analysis method and bond order-length-strength theory can be utilized to quantify the physical parameters regarding bonding identities and electronic property of metal surfaces, which allows for the study of the core-electron binding-energy shifts in alkali metals. By employing these methods and first principle calculation in this work, we can obtain the information of bond and atomic cohesive energy of under-coordinated atoms at the alkali metal surface. In addition, the effect of size and temperature towards the binding-energy in the surface region can be seen from the view point of Hamiltonian perturbation by atomic relaxation with atomic bonding.

Perspective: Bonding and electronic origin of Au atomic-undercoordination-derivacy and nanoscale-size-dependency

Atomic undercoordination entitles the inert gold even more noble at sites pertained to adatoms, defects, kinks, and skins of bulk and sized crystals with unclear mechanism. Systematic analysis of the electron emission spectra of XPS and STM/S of the undercoordinated gold atoms revealed that the 4f and 5d bands undergo quantum entrapment while the 6s level is subject to localization and polarization because of the undercoordination-induced local bond contraction and bond strength gain – named bond order-length-strength correlation and nonbonding electron polarization (BOLS-NEP). Such a bonding and electronic relaxation result in the undercoordination derivacy of properties such as its extraordinary catalytic ability that the bulk gold does never demonstrate. The BOLS-NEP in the skin-electrical-double-layer shell dictates the nanostructure size dependency of the known bulk properties such as the chemical potential, inner potential constant, elasticity, and thermal stability. The exercise not only establishes a powerful means monitoring the Hamiltonian perturbation by atomic undercoordination but also offers information on the atomic-site-resolved local bond length, bond energy, chemical potentials, energy density, and atomic cohesive energy and the associated properties.

Atomistic simulation of grain boundary migration induced by non-equilibrium solute distribution

While atomistic simulation is now a widely used method for investigating grain boundary migration, it is usually based on the so-called artificial driving force. In this study, we report a new general atomistic method for simulating grain boundary migration based on a tunable physical driving force that is induced by unbalanced solute distribution. This is motivated by the previous experimental reports that non-equilibrium distribution of solute atoms, e.g., solute atoms are more enriched/depleted in one grain relative to the other, is commonly observed during diffusion induced grain boundary migration. We show that the solute-induced driving force caused by the unbalanced free energy in the two neighboring grains strongly depends on the type of the solute atoms, which can be used to tune both the type (e.g., attraction or repulsion) and magnitude of the driving force. Furthermore, we find that different solute types (with varying atomic size and cohesive energy) interact with the grain boundary in different ways resulting in solute segregation or anti-segregation. Moreover, the lattice strain resulting from atomic size mismatch, which has been proposed to be an important driving force for diffusion induced grain boundary migration, is found to be not always needed to induce the grain boundary migration. We hope that while this study showcases a new atomistic method of simulating grain boundary migration, the results of this investigation also aids the understanding of the phenomenon of diffusion induced grain boundary migration, for which clear physical mechanisms remain elusive after decades of research.

Understanding atomic bonding and electronic distributions of a DNA molecule using DFT calculation and BOLS-BC model

Deoxyribonucleic acid (DNA) is an important molecule that has been extensively researched, mainly due to its structure and function. Herein, we investigated the electronic behavior of the DNA molecule containing 1008 atoms using density functional theory. The bond-charge (BC) model shows the relationship between charge density and atomic strain. Besides, the model mentioned above is combined with the bond-order-length-strength (BOLS) notion to calculate the atomic cohesive energy, the bond energy, and the local bond strain of the DNA chain. Using the BOLS-BC model, we were able to obtain information on the bonding features of the DNA chain and better comprehend the associated properties of electrons in biological systems. Consequently, this report functions as a theoretical reference for the precise regulation of the electrons and the bonding states of biological systems.

Effect of interatomic potentials on modeling the nanostructure of amorphous carbon by liquid quenching method

Extending from our previous work (Li et al., 2013), eight different carbon interatomic potentials, Tersoff1989, Tersoff1994, REBO-Ⅱ, AIREBO, ReaxFF, COMB3, REBO-II + S and Tersoff + S, are applied to conduct a comparative study on the nanostructure of amorphous carbon films. The amorphous carbon films at different density are modeled by LAMMPS with liquid quenching method. The atomic structure of a-C film is analyzed in terms of coordination number, radial distribution function, the bond angle distribution and Voronoi polyhedra. The effect of interatomic potentials on atomic cohesive energy and time consumption are analyzed and compared. No two potentials model the a-C film with the same atomic structure. The a-C films modeled by REBO-II + S and Tersoff + S potentials are consistent with experimental data and DFT results at density from 2.2 to 3.2 g/cm3. High sp3 carbon rate is modeled by Tersoff1994, and high sp2 carbon rate is modeled by REBO-Ⅱ and AIREBO. Lot of three-atom-rings are found when COMB3 is used. The sp3 and sp2 carbon rate are similar modeled by Tersoff1989 and ReaxFF. But there are sp1 carbon chains in a-C films modeled by ReaxFF at low density. Those results are conducive for researchers to evaluate and choose of interatomic potentials.

Anomalous H[sbnd]C bond thermal contraction of the energetic nitromethane

A systematic phonon spectrometric examination revealed that the HC phonon (2966 cm−1) undergoes blueshift under both compression and heating, but the CN (921 cm−1) and the NO (1403 cm−1) bonds undergo regular thermal redshift and compression blueshift in the Nitromethene (CH3NO2) assembly that is a solid under compression and a liquid under heating. An extension of the Grüneisen parameters integrates the phonon frequency shift to the intrinsic compressibility, thermal expansibility, specific heat, equilibrium bond length, atomic cohesive energy, and bonding energy density of the single bond which represents all of its sorts contributing to the spectral peak shift. The coupled hydrogen bond (HB, N (O):H–C), performs the same as the O:H–O of liquid water and ice I does in responding to heating. Results suggested that the combination of the N (O):H-C tension and the O:⇔:N repulsion stabilize the crystal structure and store energy, as they do in the cyclo-N5−:[4H3O+; 3H3O+ + 2NH4+] complexes.

Bond-photon-phonon thermal relaxation in the M(X, X2) (M = Mo, Re, Ta, Ge, Sn; X = S, Se, and Te).

We systematically investigated the temperature-dependent bandgap energy and Raman shift on the bond length and bond energy, Debye temperature, and atomic cohesive energy for M(X, X2) via bond relaxation methods. It is revealed that the thermal decay of both bandgap energy and phonon frequency arose from the thermal integration of the specific heat of Debye approximation. The results indicate that (i) the bandgap energy relaxation is due to the thermal excitation-induced weakening of the bond energy, and the phonon frequency was just a function of bond length and bond energy; (ii) the Debye temperature determines the nonlinear range at low temperatures; (iii) the reciprocal of the atomic cohesive energy governs the linear behavior at high temperatures. Thus, the outcomes of this study include fundamental information about photon, phonon, and the thermal properties of layered semiconductors, which are crucial to develop the new generations of thermal and electronic applications of devices based on layered semiconductors.

The BOLS-NEP theory reconciling the attributes of undercoordinated adatoms, defects, surfaces and nanostructures

This article describes a theory unifying the unusual performance of the undercoordinated adatoms, point defects, terrace edges, surfaces, and nanostructures of various shapes. The ideas of bond order-length-strength correlation and the associated nonbonding electron polarization (BOLS-NEP) feature that bonds between undercoordinated atoms contract spontaneously. Bond contraction raises the local density of charge and energy. Bond strength gain deepens the interatomic potential well to trap the core and bonding electrons deeply. In turn, the locally and densely entrapped electrons polarize those partially occupying the valence band and above pertaining to the lower-coordinated atoms. The BOLS-NEP theory reconciles the unusual behaviors of undercoordinated systems and the size dependency of nanostructures in their lattice oscillating dynamics, mechanical strength, thermal stability, photon emissivity, chemical reactivity, dielectric permeability, associated with generation of polarized Dirac fermions, serving as carriers for extraordinary catalysis, hydrophobicity, fluidity, lubricity, as well as monolayer high-T C superconductivity and topological insulator conductivity. • Atomic undercoordination shortens the local bonds and modifies the electron occupancy. • Nanocrystals prefer a core-shelled structure with a skin of two atomic layers thick. • Atomic cohesive energy dictates the thermal stability and the critical energy for phase transition. • Competition between energy density and cohesive energy transforms the Hall-Petch relationship. • Polarization dictates the catalysis, hydrophobicity, and monolayer high-T c superconductivity.

Al doped boron clusters: Planar B19Al

An optimization strategy combining global semi-empirical quantum chemistry search with all-electron density functional theory was adopted to determine the lowest energy structure of B19Al clusters. B19Al is a nearly perfect planar, which is remarkably different from that of tubular neutral B20 cluster. The Al atom occupies a peripheral position of the planar, which results from the difference in atomic size and cohesive energy between aluminum and boron atoms. Meanwhile, the planarity of B19Al cluster is attributed to s-p2 hybridization. Some properties, including chemical bonding, HOMO–LUMO gaps, molecular orbital distribution, electric dipole moments, and charge transfer and distribution, are discussed. The doped planar boron clusters can be created by doping with Al atom.

Heterojunction bond relaxation and electronic reconfiguration of WS2- and MoS2-based 2D materials using BOLS and DFT

Density functional theory (DFT) calculations have revealed the essential nature of bond relaxation and electronic reconfiguration in (GaAs, Graphene, InSe)-(WS2, MoS2) layered heterojunctions. The bandgap lies within the range 0.01 ∼ 1.0 eV, which may be suitable for photocatalytic applications. We have also established a relationship between the atomic coordination density and the surface strain of two-dimensional heterojunctions. Moreover, the interfacial atomic cohesive energy and the bond energy density varies from case to case. These findings may lead to new materials for related fields.

Bond−Energy−Electron Relaxation of BeN Nanoclusters and BeX Alloys

AbstractBy combining bond order‐length‐strength (BOLS) notion and density functional theory (DFT) calculations, the bond−energy−electron relaxtion of BeN nanoclusters and BeX (C, S, B, Cl, Cu, Co, Te) alloys are studied. The results show that the size and shape of the Be nanoclusters will cause the binding energy (BE) shift, the local densification of electrons and quantum entrapment. Actions exemplified the atomic coordination ratio and the BE of BeX alloys can predict the quantitative information regarding the change of the bond length, local bond strain, bond energy density and atomic cohesive energy.

Piezoelectric and pyroelectric properties of intrinsic GaN nanowires and nanotubes: Size and shape effects

Gallium nitride (GaN) nanowires and nanotubes possess extraordinary device ability of converting wasted energy into harvestable electricity in terms of their piezoelectricity and pyroelectricity. From the perspective of atomic cohesive energy, we present a model to clarify the physical origin of the size- and shape-dependency of the piezoelectric and pyroelectric properties for intrinsic GaN nanowires and nanotubes. It is shown that both the piezopotential and the pyropotential increase with the inverse of GaN nanocrystal size or with the shape factor. The influence of size and shape becomes more significant for nanotubes with smaller size or wall thick-to-size ratio and may enhance both potentials by up to dozens of times or even more. Such size and shape effects originate from the synergetic effects of nanoscale dielectricity, piezoelectricity and thermoelasticity where the piezoelectricity plays a more important role than the other two factors. Moreover, high piezopotential and pyropotential in GaN nanotubes render them appealing in the design of novel nanogenerators in comparison with the most commonly used nanowires.

A Stillinger-Weber Potential for InGaN

Reducing defects in InGaN films deposited on GaN substrates has been critical to fill the “green” gap for solid-state lighting applications. To enable researchers to use molecular dynamics vapor deposition simulations to explores ways to reduce defects in InGaN films, we have developed and characterized a Stillinger-Weber potential for InGaN. We show that this potential reproduces the experimental atomic volume, cohesive energy, and bulk modulus of the equilibrium wurtzite / zinc-blende phases of both InN and GaN. Most importantly, the potential captures the stability of the correct phase of InGaN compounds against a variety of other elemental, alloy, and compound configurations. This is validated by the potential’s ability to predict crystalline growth of stoichiometric wurtzite and zinc-blende InxGa1-xN compounds during vapor deposition simulations where adatoms are randomly injected to the growth surface.

Large scale structural optimization of trimetallic Cu–Au–Pt clusters up to 147 atoms

The stable structures of Cu–Au–Pt clusters up to 147 atoms are optimized by using an improved adaptive immune optimization algorithm (AIOA-IC method), in which several motifs, such as decahedron, icosahedron, face centered cubic, sixfold pancake, and Leary tetrahedron, are randomly selected as the inner cores of the starting structures. The structures of Cu8AunPt30-n (n=1–29), Cu8AunPt47-n (n=1–46), and partial 75-, 79-, 100-, and 147-atom clusters are analyzed. Cu12Au93Pt42 cluster has onion-like Mackay icosahedral motif. The segregation phenomena of Cu, Au and Pt in clusters are explained by the atomic radius, surface energy, and cohesive energy.

Influence of noble metal dopants (M = Ag, Au, Pd or Pt) on the stable structures of bimetallic Co-M clusters

The core-shell and well-mixed morphologies of Co-M (M = Ag, Au, Pd or Pt) clusters are investigated. The interatomic interaction of these clusters is described by the many-body Gupta potential, and the stable structures are optimized using adaptive immune optimization algorithm. Results show that all 55-atom Co-Au and Co-Pd clusters adopt Mackay icosahedral motifs, but Co-Ag and Co-Pt clusters have more configurations. The number of bonds indicates that Co-Ag, Co-Au and Co-Pd clusters take the core-shell structures. In these core-shell structures, Co atoms occupy the inner core, and Ag and Pd atoms tend to scatter on the surface, but Au atoms prefer packing together, which is explained by atomic radii, cohesive energy and surface energy. However, the investigated Co-Pt clusters favor well-mixed pattern. Furthermore, there exists difference among the relative stability of these clusters by energy analysis. Moreover, the influence of the noble metals on the structures of Co13Mn (n = 1–41) clusters are studied. The atomic distribution of Co and noble metals in Co13Mn clusters is analyzed, which is consistent with that in 55-atom Co-M clusters.

Breaking surface states causes transformation from metallic to semi-conducting behavior in carbon foam nanowires

Carbon foam nanowires (CFNWs), which are mixed sp2/sp3 hybridized microporous one-dimensional structures, have received much attention in the past two decades. In the present work, first-principle and molecular dynamics (MD) calculations revealed that the surface states causes the metallicity of CFNWs with small size, which demonstrates a Dirac cone-like dispersion near Γ in the Brillouin zone, while the metallicity of large size CFNWs are caused by the bulk states. However, hydrogenation of the CFNWs turns the metallicity into semiconducting with an expansion of the band gap by 0.15–1.5 eV. Interestingly, the metallicity is enhanced when hydrogenation on the top of the CFNWs. Atomic cohesive energy analysis suggests that the CFNWs are energetically favorable up to its melting point at 2200 K. When heating above the melting point, CFNWs transit into multi-walled carbon nanotubes (MWCNTs), agreeing with experimental observations. These findings indicate the feasibility of metallic-semiconductive transition, which have potential applications in nanoscale devices, hydrogen storage and the preparation of MWCNTs.