Diatomic Energy Research Articles

Silicate glass fracture surface energy calculated from crystal structure and bond-energy data

We present a novel method to predict the fracture surface energy, γ, of isochemically crystallizing silicate glasses using readily available crystallographic structure data of their crystalline counterpart and tabled diatomic chemical bond energies, D0. The method assumes that γ equals the fracture surface energy of the most likely cleavage plane of the crystal. Calculated values were in excellent agreement with those calculated from glass density, network connectivity and D0 data in earlier work. This finding demonstrates a remarkable equivalence between crystal cleavage planes and glass fracture surfaces.

Diatomic molecular energy spectra and thermodynamic properties of exponential inversely quadratic plus improved deformed exponential-type potential

By employing the Pekeris-type approximation to deal with the centrifugal term, we study the thermodynamic properties and approximate analytical solutions of the Schrödinger equation with the exponential inversely quadratic plus improved deformed exponential-type potential using parametric Nikiforov–Uvarov method and hypergeometric functional analysis method. The complex eigen energy equation was presented in a closed and compact form and extended to study partition function and other thermodynamic properties. The total normalized wave functions were also obtained and expressed in terms of hypergeometric Jacobi polynomial. The mathematical accuracy of analytical calculation can be verified consistently by comparing numerical data and results of different arbitrarily l state. The potential also reduces to improved deformed exponential-type potential as a special case. We calculated energy spectra for some selected diatomic molecules namely: Silicon Flouride (SiF+ (X1∑+), Oxygen molecule O2+ (X2∏g), Nitrogen molecule, N2+ (X1∑g+), Sulphur chloride SCl and Rubidium hydride RbH using standard molecular spectroscopic constants as applied to the two methods. The results show that the energy eigenvalues for these selected diatomic molecules are in excellent agreement using the two methods and also increases with an increase in quantum state.

Simulation of Internal Defects in TKX-50 Crystals.

1,1'-Dihydroxy-5,5'-bi-tetrazolium dihydroxylamine salt (TKX-50) is a new type of high-energy low-sense explosive with great application value, but TKX-50 made directly from the reaction has problems such as irregular crystal morphology and relatively large length-diameter, and these factors seriously affect the sensitivity of TKX-50 and limit its large-scale application. The internal defects of TKX-50 crystals have a great influence on their weakness, and studying its related properties is of great theoretical significance and application value. To further investigate the microscopic properties of TKX-50 crystals and to explore the connection between microscopic parameters and macroscopic susceptibility, this paper reports the use of molecular dynamics simulations to construct TKX-50 crystal scaling models with three types of defects-vacancy, dislocation and doping-and conducts molecular dynamics simulations. The influence of TKX-50 crystal defects on the initiation bond length, density, bonding diatomic interaction energy, and cohesive energy density of the crystal was obtained. The simulation results show that the models with a higher bond length of the initiator bond and higher percentage activated the initiator's N-N bond and lowered the bond-linked diatomic energy, cohesive energy density, and density corresponding to higher crystal sensitivities. This led to a preliminary connection between TKX-50 microscopic model parameters and macroscopic susceptibility. The results of the study can provide a reference for the design of subsequent experiments, and the research method can be extended to the research work on other energy-containing materials.

Jost states for the Deng-Fan potential

Deng-Fan Potential is well known in describing diatomic molecular energy spectra and electromagnetic transitions. An irregular solution for the Deng-Fan potential is constructed by adapting the differential equation approach to the problem. The Jost function thus obtained is applied to find bound state energies and the scattering phase shifts for nuclear systems. Also phase function method has been applied in parallel with that of Jost function technique for similar investigation. Results show close agreement with the experimental ones. Exploiting the phase parameters the elastic scattering cross sections have been estimated.

Tuning the Site-to-Site Interaction in Ru-M (M=Co, Fe, Ni) Diatomic Electrocatalysts to Climb up the Volcano Plot of Oxygen Electroreduction.

The modulating of the geometric and electronic structures of metal-N-C atomic catalysts for improving their performance in catalyzing oxygen reduction reactions (ORRs) is highly desirable yet challenging. We herein report a delicate "encapsulation-substitution" strategy for the synthesis of paired metal sites in N-doped carbon. With the regulation of the d-orbital energy level, a significant increment in oxygen electroreduction activity was demonstrated in Ru-Co diatomic catalyst (DAC) compared with other diatomic (Ru-Fe and Ru-Ni) and single-atomic counterparts. The Ru-Co DAC efficiently reduces oxygen with a halfwave potential of 0.895 V vs RHE and a turnover frequency of 2.424 s-1 at 0.7 V, establishing optimal thermodynamic and kinetic behaviors in the triple-phase reaction under practical conditions. Moreover, the Ru-Co DAC electrode displays bifunctional activity in a gas diffusion Zn-air battery with a small voltage gap of 0.603 V, outperforming the commercial Pt/C|RuO2 catalyst. Our findings provide a clear understanding of site-to-site interaction on ORR and a benchmark evaluation of atomic catalysts with correlations of diatomic structure, energy level, and overall catalytic performance at the subnanometer level.

Combining ab initio and machine learning method to improve the prediction of diatomic vibrational energies

AbstractThrough the comprehensive analysis of ab initio and experimental results of a large number of diatomic systems, the systematic deviation of ab initio method in vibrational energies prediction caused by physical/mathematical simplification is located. A joint ab initio and machine learning method based on information across molecules is proposed to deal with the problem. Starting from an ab initio model, and then systematically modifying it through machine learning, the vibrational energies prediction of many diatomic systems (SiC, HBr, NO, PC, N2, SiO, O2, ClF, etc.) have been improved, and significantly surpassed the more complex ab initio model. In addition to the improvement of accuracy, the new method also greatly reduces the computational expense, and is applicable for the systems without experimental data.

Internal nucleation tendency and crystal surface energy obtained from bond energies and crystal lattice data

We present an easy-to-apply method to predict structural trends in the internal nucleation tendency of oxide glasses. The approach is based on calculated crystal fracture surface energies derived from easily accessible diatomic bond energy and crystal lattice data. The applicability of the method is demonstrated on literature nucleation data for isochemically crystallizing oxide glasses.

Molecular dynamics study on the effect of temperature on the properties of TATB and PBX

In order to study the effect of temperature on the properties of PBX explosive, three models of TATB pure crystal, JB-9014 coated and mixed structure were established by using material studio (MS) software. Molecular dynamics calculations were carried out at different temperatures (255k, 275k, 295k, 315K, 335k and 355k) using compass II force field. The initiation bond length, bonding diatomic energy, cohesive energy density and mechanical properties of different structures were obtained and compared. The results show that compared with TATB pure crystal, the two PBX structures have less change in the initiation bond length, and the density of bonding diatomic energy and cohesive energy is significantly reduced, and the sensitivity is higher. The results of mechanical properties show that the two PBX structures have less rigidity, stronger elasticity and better ductility compared with TATB pure crystal, which is conducive to the processing and transportation of explosives. In addition, with the increase of temperature, the sensitivity of the two PBX structures increases, the stability becomes worse, and the influence on the mechanical properties tends to be complex.

An approach to determine the diatomic vibrational energy levels: application to LiH, NO and CO molecules

This work presents the systematic calculation of vibrational energy levels, for diatomic molecules through an alternative approach, reposed on the Floquet representation analysis. The Morse potential function has been employed to solve the Schrodinger equation, and to obtain the vibrational energy levels of diatomic systems. As an illustration, the numerical energy values of some molecules have been computed, and compared to those of literature, revealing a good agreement, and showing the accuracy of our approach.

A New Mixing of Nonlocal Exchange and Nonlocal Correlation with Multiconfiguration Pair-Density Functional Theory.

We propose a hybrid multiconfiguration pair-density functional theory (HMC-PDFT) that is a weighted average of complete-active-space self-consistent-field (CASSCF) and multiconfiguration pair-density functional theory (MC-PDFT) energies with a semiempirical parameter to control the fraction of CASSCF energy. We also explore a more general two-parameter hybrid method with a scaled correlation energy that allows us to compare to the recently proposed λ-MC-PDFT method. We scan the parameter space for the scaled-correlation method using test sets consisting of electronic excitation energies and diatomic bond energies, and we find no significant improvement by introducing the scaling parameter. We find that unscaled HMC-PDFT offers significantly improved accuracy over both CASSCF and the original MC-PDFT for a wide range of systems, and we present as an example of this approach "tPBE0", the "translated" MC-PDFT generalization of the popular PBE0 hybrid Kohn-Sham density functional.

Constructing feed-forward artificial neural networks to fit potential energy surfaces for molecular simulation of high-temperature gas flows.

Kinetic rates for thermochemical nonequilibrium models are generally computed from quasiclassical trajectory (QCT) calculations on accurate ab initio potential energy surfaces (PES). In this article, we use a feed-forward artificial neural network (ANN) to fit existing single-point energies for N_{2}+N_{2} interactions [Bender et al., J. Chem. Phys. 143, 054304 (2015)JCPSA60021-960610.1063/1.4927571] to construct a PES suitable for molecular simulation of high-temperature gas flows. We then perform detailed comparisons with a widely used N_{4} PES that was built using the permutation invariant polynomials (PIP) method. Specific physical considerations in the construction of the ANN for this application are detailed. Translation, rotation, and permutation invariance are precisely satisfied by mapping the interatomic distances onto a set of permutation invariant inputs, known as fundamental invariants (FI) that generate the permutation invariant polynomial ring. The diatomic energy is imposed by decomposing the total potential energy into a sum of a two-body and a many-body energy contribution. To obtain the correct dynamical behavior with the most basic, yet computationally efficient ANN, spurious long-distance interactions must be removed to avoid incorrect physical behavior at the dissociation threshold. We use a simple apodization function to smoothly taper off to zero any residual many-body interaction at large separations. Both accuracy and performance of the FI-ANN PES are assessed. QCT calculations are used to compute dissociation probabilities and vibrational energy distributions at various equilibrium temperatures. Excellent agreement with the results obtained from the PIP PES is found. For our test case, the ANN PES is also significantly more computationally efficient than the PIP PES at comparable root-mean-square error levels.

Diatomic molecules energy spectra for the generalized Mobius square potential model

The modified version of the generalized Mobius square (GMS) potential has been obtained by employing the dissociation energy and equilibrium bond length as explicit parameters. The potential parameters have been defined in terms of the molecular parameters. The modified GMS potential has also been used to model internuclear interaction potential curves for different states of diatomic molecules. Also, we have obtained the rotational–vibrational energy spectra of the new GMS potential model, both analytically and numerically for the different diatomic molecules. This was done by employing a Pekeris-type approximation scheme and an appropriate coordinate transformation to solve the Schrodinger equation. Our results have been compared with the experimental Rydberg–Klein–Rees (RKR) data and its corresponding average absolute deviations in terms of the dissociation energy computed. The effects of the vibrational and rotational quantum numbers on the rotational–vibrational energies for the different states of the various diatomic molecules have also been discussed. This paper has shown to be highly relevant to the studies of thermodynamic and thermochemical functions of diatomic molecules.

Systematic Approach to Compute the Vibrational Energy Levels of Diatomic Molecules

In continuation of our previous paper of the anharmonic potentials analysis through the Floquet representation, we performed in this work a systematic calculation of the diatomic vibrational energy levels as well as the corresponding wave functions. The solution of Schrodinger equation according to Morse potential, which is a suitable model to describe the diatomic vibrational spectra, has been introduced; thus the explicit formulas to the second order have been established. As an illustration, the dissociation energies of some molecules species (i.e. ScN, LiH, Cl2 and NO) have been computed, as well as the wave functions and the corresponding probability densities, relating to the (ScN) molecule have been represented. Comparisons of our results with those of literature have been made.

Assessment of DFT Methods for Transition Metals with the TMC151 Compilation of Data Sets and Comparison with Accuracies for Main-Group Chemistry.

In the present study, we have gathered a collection (that we term TMC151) of accurate reference data for transition-metal reactions for the assessment of quantum chemistry methods. It comprises diatomic dissociation energies and reaction energies and barriers for prototypical transition-metal reactions. Our assessment of a diverse range of different types of DFT methods shows that the most accurate functionals include ωB97M-V, ωB97X-V, MN15, and B97M-rV. Notably, they have also been previously validated to be highly robust for main-group chemistry. Nevertheless, even these methods show substantially worse accuracies for transition metals than for main-group chemistry. For less accurate methods, there is not a good correlation between their accuracies for main-group and transition-metal chemistries. Thus, in the development of new DFT, it is important to assess the accuracies for both types of data. In this regard, we have formulated the TMC34 model for efficient assessment of the performance for transition metals, which complements our previously developed MG8 model for main-group chemistry. Together, they provide a cost-effective means for initial assessment of new methodologies.

Scattering of cold He4 on He4Li6,7 and He4Na23 molecules

We predict $s-$wave elastic cross-sections $\sigma$ for low-energy atom-molecule collisions with kinetic energies up to 40 mK, for the $^4$He collision with weakly bound diatomic molecules formed by $^4$He with $^7$Li, $^6$Li and $^{23}$Na. Our scattering calculations are performed by using diatomic and triatomic molecular binding energies obtained from several available realistic models as input in a renormalized zero-range model, as well as a finite-range one-term separable potential in order to quantify the relevance of range corrections to our predictions. Of particular relevance for possible experimental realization, we show the occurrence of a zero in $\sigma$ for the collision of cold $^4$He on $^4$He$-^{23}$Na molecule below 20 mK. Also our results for the elastic collision $^4$He on $^4$He$-^{6,7}$Li molecules suggest that $\sigma$ varies considerably for the realistic models studied. As the chosen molecules are weakly bound and the scattering energies are very low, our results are interpreted on the light of the Efimov physics, which explains the model independent and robustness of our predictions, despite some sensitivity on the potential range.

On the Unusual Synclinal Conformations of Hexafluorobutadiene and Structurally Similar Molecules.

An explanation is presented for the unusual conformations of some molecules that contain the C═C-C═C core, namely, butadienes, biphenyls, and styrenes. Small substituents often induce a synclinal conformation, which brings the substituents into close proximity, and sometimes, there is no anticlinal minimum at all. This would not be predicted from steric repulsion arguments nor would it be expected that atoms that are nonbonded in a Lewis structure would approach closer than the sum of their van der Waals radii. Atomic energies calculated according to the quantum theory of atoms in molecules (QTAIM) do not show a consistent pattern for these structurally similar molecules, nor are intersubstituent bond paths consistently found, nor favorable diatomic interaction energies calculated using the interacting quantum atoms (IQA) scheme. Instead, the synclinal conformations are found to be driven by the attraction energy of the electron distribution of the carbon atoms and the nuclei of the molecule.

Size-, Shape-, and Composition-Dependent Model for Metal Nanoparticle Stability Prediction.

Although tremendous applications for metal nanoparticles have been found in modern technologies, the understanding of their stability as related to morphology (size and shape) and chemical ordering (e.g., in bimetallics) remains limited. First-principles methods such as density functional theory (DFT) are capable of capturing accurate nanoalloy energetics; however, they are limited to very small nanoparticle sizes (<2 nm in diameter) due to their computational cost. Herein, we propose a bond-centric (BC) model able to capture cohesive energy trends over a range of monometallic and bimetallic nanoparticles and mixing behavior (excess energy) of nanoalloys, in great agreement with DFT calculations. We apply the BC model to screen the energetics of a recently reported 23 196-atom FePt nanoalloys ( Yang et al. Nature 2017 , 542 , 75 - 79 ), offering insights into both segregation and bulk-chemical ordering behavior. Because the BC model utilizes tabulated data (diatomic bond energies and bulk cohesive energies) and structural information on nanoparticles (coordination numbers), it can be applied to calculate the energetics of any nanoparticle morphology and chemical composition, thus significantly accelerating nanoalloy design.

Studies on order – Disorder transition, lattice expansion and ionic conductivity in aliovalent cation substituted Sm2Zr2O7 System

The effect of simultaneous aliovalent cation substitution on a pyrochlore lattice in (Sm,Zr)2-x(Sc,Ce)xO7 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) was investigated by X-ray diffraction in ambient and high-temperature conditions, electron microscopy, Raman spectroscopy and impedance spectroscopy. The samples were prepared by a conventional high temperature ceramic route. Due to comparable sizes of the ions involved, both the substituent ions diffused randomly into both cation sites leading to an order-to-disorder transition. The lattice thermal expansion coefficient decreases continuously with increased aliovalent cations substitutions which is mainly attributed to the increased diatomic bond energy of the average cation-oxygen bond, unlike the usual trends observed in the systems having phase transition from ordered pyrochlore to disordered fluorite system. The trends in ionic conductivity suggest that it is more governed by the co-operative behaviour of the mobile charge carriers. in the higher substitutions leading to higher activation energies. Hence in the case of pyrochlore type composition, in addition to the lattice disordering, co-operative behaviour of the mobile charge carriers and ionization energy of the individual bond play an important part in determining the electrical behaviour of the system.

Hermitian “chemical” Hamiltonian: an alternative ab initio method

Some previous results of the present author are combined in order to develop a Hermitian version of the “Chemical Hamiltonian Approach.” In this framework the second quantized Born–Oppenheimer Hamiltonian is decomposed into one- and two-center components, if some finite basis corrections are omitted. (No changes are introduced into the one- and two-center integrals, while projective expansions are used for the three- and four-center ones, which become exact only in the limit of complete basis sets.) The total molecular energy calculated with this Hamiltonian can then presented as a sum of the intraatomic and diatomic energy terms which were introduced in our previous “chemical energy component analysis” scheme. The corresponding modified Hartree–Fock–Roothaan equations are also derived; they do not contain any three- and four-center integrals, while the non-empirical character of the theory is conserved. This scheme may be useful also as a “layer” in approaches like ONIOM.

Full vibrational spectra of some electronic states of NaLi molecule using a difference converging method

For most diatomic electronic states, it is very difficult to obtain the accurate vibrational spectra of the highly-excited states directly by using the modern experimental techniques and quantum theories. Based on the general expression of diatomic molecular vibrational energy, the difference converging method (DCM) is used to give a new analytical expression in this paper. By using ten known vibrational energies, the full vibrational spectra, the vibrational spectroscopic constants of the highly-excited states, and the dissociation energy can be predicted for a diatomic electronic state. In this study, the full vibrational spectra of the electronic states 31Π, 41Π and A1Σ+ of NaLi molecule are studied with the DCM and the new formula. Results show that all the vibrational levels given in the experiments can be reproduced with an error rate less than 0.02 percent in our study. In addition, By comparing with the reported experimental results, we find 26, 45 and 31 new vibrational levels for 31Π, 41Π and A1Σ+ of NaLi molecule, respectively.