Unbonded Atoms Research Articles

Training dependency of neural network interatomic potential for molecular dynamics simulation of Ru-Si-O mixed system

We investigated the training dependency of neural network interatomic potentials for molecular dynamics simulation of a Ru–Si–O mixed system. Our neural network interatomic potential was improved using a data augmentation technique for the training dataset, including data points of reference energies and forces related to reference structures. We demonstrated that the data augmentation technique, focusing on the lattice expansion coefficient of bulk structures in the training dataset, requires moderation to ensure optimal training of the neural network interatomic potential. We found that Ru/SiO2 interfaces were accurately represented using the neural network interatomic potential trained with Ru and SiO2 surfaces in addition to Ru/SiO2 interfaces. In the case of modeling Ru/SiO2 interfaces including unbonded atoms, training the surfaces with unbonded atoms is effective in generalizing the neural network interatomic potential. Our demonstration and finding shed light on the pivotal role of the training dataset on the development of the neural network interatomic potential for the Ru–Si–O mixed system.

Dynamical and mechanical stability, electronic properties, bonding and weak interactions analysis of new compounds MgS2 and MgSe2 in [formula omitted] space group structure: Ab initio study

The main objective of this work is to highlight several physical behaviors of two new compounds (MgS2 and MgSe2) in the cubic structure of the Pa-3 space group, particularly their mechanical and dynamical stabilities, their electronic behaviors and to provide a detailed analysis of bonding between the different atoms and the identification of weak interactions that occur between unbonded atoms. The found results have shown that the two studied compounds are mechanically and dynamically stable, which confirms their presence in the Pa-3 space group structure. The values of the lattice parameter of both compounds are close to the theoretical comparison ones. 3D directional analysis of several mechanical quantities (E, G and υ) has shown that both compounds are elastically anisotropic. The study of the electronic properties has been carried out by TB-mBJ potential, which accurately estimates the band gap energy. The found results have shown that the value of the direct band-gap is close to that of the indirect one, which highlights the optoelectronic importance of these two new compounds. QTAIM analysis has shown that S-S and Se-Se bonds have a strong covalent character, while Mg-S and Mg-Se are ionic. Using the NCI method, weak interactions analysis has made it possible to locate all weak/strong interactions that exist in the structure of the two studied compounds and to identify their attractive/repulsive natures.

Elements of the third kind and the spin-dependent chemical force

A lively philosophical debate has lately arisen over the nature of elementhood in chemistry. Two different senses in which the technical term ELEMENT is currently in use by chemists have been identified, leaving chemistry open to the logical fallacy of equivocation. This paper introduces a third, more elemental candidate: the high-enthalpy short-lived unbonded atom. An enthalpy index based on free-atoms-as-elements is established, whereby one can monitor the degree to which an atom’s spin-based attractive force is implemented exo-enthalpically when the atom binds chemically to others. Enthalpy indexing shows that the strength of an atom’s attractive force is proportional to its spin angular momentum. Vibrational spectroscopy shows that the force varies inversely as the fourth power of the inter-atom distance. Both features differentiate the chemical force from the stronger electromagnetic force and from the weaker Van der Waals force.

Rydberg–London potential for diatomic molecules and unbonded atom pairs

We propose and test a pair potential that is accurate at all relevant distances and simple enough for use in large-scale computer simulations. A combination of the Rydberg potential from spectroscopy and the London inverse-sixth-power energy, the proposed form fits spectroscopically determined potentials better than the Morse, Varnshi, and Hulburt-Hirschfelder potentials and much better than the Lennard-Jones and harmonic potentials. At long distances, it goes smoothly to the London force appropriate for gases and preserves van der Waals's "continuity of the gas and liquid states," which is routinely violated by coefficients assigned to the Lennard-Jones 6-12 form.

Electron states at abrupt metal-GaAs(110) interfaces

The electronic properties of forming metal/GaAs(110) interfaces ( M = Ag, Cu, Ga, In), determined from photoemission yield spectroscopy, are compared and discussed. They are governed by electron interface states associated with i) the restructured semiconductor surface unbonded atoms ii) the formation of bonds between the metal atoms and the atoms of the first GaAs layer. Although the systems form with different atomic arrangements at the interface, the Schottky barrier depends only slightly on the metal.

The covalent bond in silicon

A detailed electron distribution study of the covalent bond in silicon is discussed. The study is based on the strategy employed earlier to define the covalent bond in diamond, and estimates of the bonded-atom scattering power, including results for 222, that have been obtained in three different X -ray experiments at room temperature are considered. Two of these involve the conventional approach via intensity measurement, that of Gottlicher & Wolfel (G. W. ) on powders and that of DeMarco & Weiss (D. M. W. ) on perfect single crystals, while the third by Hattori, Kuriyama, Katagaw a & Kato (H. K. K. K. ) involves the measurement of spacing in X -ray Pendellösung fringes observed in wedge-shaped perfect crystal specimens and their interpretation by the dynamical theory of Kato. It is shown that only the results obtained by H. K. K. K. are capable of detailed analysis in term s of the criteria now available from the earlier study of diamond, from which we conclude that the fringe-spacing method has yielded data for the low-angle reflexions which are superior to the data obtained m re conventionally by G. W. and D. M. W. The covalent bond in silicon is described comprehensively by two non-spherical components as in diamond. The major (antisymmetric) component involves the radial functionF3(r) = 1⋅11r2exp (─ 0⋅88r2), and the minor (cubo-centrosymmetric) the functionG4(r) = ─ 0⋅321r2exp (─0⋅88r2). The origin of these components lies in an electron redistribution of the spherical unbonded atom involving 0⋅127 electron per bond, and this leads to a peak of + 0⋅25 e/Å3at the mid-point of the covalent bond. The consequences of this study are considered in relation to future attempts to examine aspects of electron distribution in atoms of different weight. The suitability of diamond and silicon as standards for scaling intensity data to the strict absolute basis so essential to such studies is also noted.

The covalent bond in diamond

The generalized X -ray structure factor described in the preceding paper is used in an electron distribution study of the covalent bond in diamond. Numerical analysis is based on the X -ray powder measurements of G‪‪‪‪‪‪‪‪‪öttlicher & W‪‪‪‪‪‪‪‪‪ölfel and on Renninger’s measurement of the ‘forbidden’ reflexion 222. The T d symmetry of the atomic sites in diamond is used to express the charge distribution of the bonded atom as a simple sum of components consisting of radial functions combined with the appropriate Kubic Harmonics (KH) of Von der Lage & Bethe. The analysis is conducted in terms of the f (exp) values which typify the bonded-atom scattering power at room temperature. It is assumed that contributions to f (exp) made by the spherical component of the total bonded-atom charge distribution can be accurately described by combining ( a ) the theoretical f̄ values given by the Hartree—Fock approximation to the spherically averaged distribution of the isolated atom in its ground state with ( b ) the isotropic temperature factor exp (─0.20 sin 2 θ/λ 2 ). The non-spherical features of f (exp) reveal two other important components in the total distribution of the bonded atom. The major component, possessing antisymmetric character, combines the third order KH with the radial function F 3 ( r ) = 7.5 r 2 exp (─2.2 r 2 ): this component accounts quantitatively for the 222 reflexions and for the grosser nonspherical features of f (exp) for odd-index reflexions. The subsidiary component, of cubic (centro-) symmetry, combines the fourth order KH with the function G 4 ( r ) = -2.0 r 2 exp (─ 2⋅2 r 2 ): this accounts for finer nonspherical features of f (exp) for both odd- and even-index reflexions. These two nonspherical components are associated directly with the covalent bond in diamond. Their origin lies in an electron redistribution of the spherical unbonded atom involving only 0.087 electron per bond. It is shown that the covalent bond corresponds to a mid-bond peak of +0.64 e/Å 3 . Fourier representations of the bonding redistribution in (11̄0) of the structure are presented. It is shown that the f (exp) values for sin θ/λ < 0⋅7 Å -1 allow the electron density associated with covalent bonding to be resolved to a standard deviation of ca . 0.018 e/Å 3 .