Bond Length Distribution Research Articles

Investigation of phase separation mechanism in AlCoCrFeMo0.05Ni2 high-entropy alloy by first-principles calculations

AlCoCrFeMo0.05Ni2 high-entropy alloy (HEA) has great potential for high-temperature applications. However, its FCC matrix will decompose during annealing, which seriously limits its high-temperature applications. Here, the lattice distortion, Gibbs free energy change, phonon spectra, density of states, and bond length distribution of the FCC matrix were calculated by first-principles calculations. The findings indicate that the primary barrier to the formation of a single homogeneous solid solution in the alloy is more closely associated with Gibbs free energy rather than the degree of lattice distortion. The vibration frequency of Al is not in sync with the overall structure, making it prone to desolvation at elevated temperatures. Furthermore, an analysis of bond lengths reveals that the Al–Ni bond length is significantly shorter than the theoretical value, facilitating the formation of a (Ni, Al)-rich phase. In contrast, the longer bond lengths of Al–Cr and Al–Mo facilitate the detachment of Cr and Mo from the (Ni, Al)-rich phase, resulting in the formation of (Cr, Mo)-rich phase. This in-depth investigation sheds light on the phase decomposition mechanism of high-entropy alloys, offering valuable insights for future research in this field.

Nanoscale Localized Phonons at Al2O3 Grain Boundaries.

Nanoscale defects like grain boundaries (GBs) would introduce local phonon modes and affect the bulk materials' thermal, electrical, optical, and mechanical properties. It is highly desirable to correlate the phonon modes and atomic arrangements for individual defects to precisely understand the structure-property relation. Here we investigated the localized phonon modes of Al2O3 GBs by combination of the vibrational electron energy loss spectroscopy (EELS) in scanning transmission electron microscope and density functional perturbation theory (DFPT). The differences between GB and bulk obtained from the vibrational EELS show that the GB exhibited more active vibration at the energy range of <50 meV and >80 meV, and further DFPT results proved the wide distribution of bond lengths at GB are the main factor for the emergence of local phonon modes. This research provides insights into the phonon-defect relation and would be of importance in the design and application of polycrystalline materials.

Effects of Na/K-Cl Salts on Hydrolysis of Aluminosilicate Glass Using Ab Initio Molecular Dynamics.

The structural and chemical modifications on the surface of pure and alkali-doped aluminosilicate (AS) glasses due to hydrolysis are investigated using ab initio molecular dynamics. The effects of water on the glass network are fully elucidated by analyzing the short- and intermediate-range structural orders embedded in the pair distribution function, bond length and angle distribution, coordination number, and interatomic bonding. A novel concept of total bond order is used to quantify and compare the strength of bonds in hydrated and unhydrated glasses. We show that AS glass is hydrolyzed by water diffusion near the surface and by proton (H+) transfers into the bulk, which increases with time. Hence, a dissolved glass-water interface becomes rich in Si-OH and Al-OH. The alkali ions associated with the nonbridging oxygen accelerate the hydrolysis by facilitating water and H+ diffusion. Al is more impacted by hydrolysis than Si, resulting in greater variation in the Al-O bond order than Si-O. Doping of NaCl and KCl enhances the ionization of water and the hydrolysis of ASs with increased salt concentration. The KCl doping ionizes more water molecules and causes more degradation of the glass network than NaCl. Co-doping of Na and K results in a mixed alkali effect due to complex interatomic bonding from different-sized ions. These exceptionally detailed findings in highly complex glasses with varying salt compositions provide new and unprecedented atomistic insights that can help to understand the hydrolysis and dissolution mechanisms of ASs and other silicate glasses.

(Non)Resonance Bonds in Molecular Dynamics Simulations: A Case Study concerning C60 Fullerenes.

In the case of certain chemical compounds, especially organic ones, electrons can be delocalized between different atoms within the molecule. These resulting bonds, known as resonance bonds, pose a challenge not only in theoretical descriptions of the studied system but also present difficulties in simulating such systems using molecular dynamics methods. In computer simulations of such systems, it is often common practice to use fractional bonds as an averaged value across equivalent structures, known as a resonance hybrid. This paper presents the results of the analysis of five forms of C60 fullerene polymorphs: one with all bonds being resonance, three with all bonds being integer (singles and doubles in different configurations), one with the majority of bonds being integer (singles and doubles), and ten bonds (within two opposite pentagons) valued at one and a half. The analysis involved the Shannon entropy value for bond length distributions and the eigenfrequency of intrinsic vibrations (first vibrational mode), reflecting the stiffness of the entire structure. The maps of the electrostatic potential distribution around the investigated structures are presented and the dipole moment was estimated. Introducing asymmetry in bond redistribution by incorporating mixed bonds (integer and partial), in contrast to variants with equivalent bonds, resulted in a significant change in the examined observables.

Theoretical Insights on Pb‐Free Rhombohedral CsGeI3 over Cubic CsMX3 (M‐: Pb, Sn, Ge, and X‐: Cl, Br, I) Perovskite‐Based Single‐Junction Solar Cell with Efficiency &gt;30%

Herein, density functional theory‐based comparative studies on cubic CsMX3 (M‐: Pb, Sn, Ge; X‐: Cl, Br, I) and rhombohedral CsGeI3 perovskites are reported. The structural stability indicator analysis shows that Ge‐based perovskites may exhibit small rhombohedral distortion led by lone pair (4) electrons on off‐centering Ge atom. The role of lone pair on Ge atom in rhombohedral distortion is corroborated by bond length, electronegativity, and charge density distributions. Nearly agreeable bandgap () values are noticed for cubic CsPbX3 (X‐: Cl, Br, I) and rhombohedral CsGeI3, and the corresponding values are 3.04, 2.30, 1.72, and 1.45 eV, respectively. The effect of Jishi et al. reparameteried Tran–Blaha‐modified Becke–Johnson exchange‐correlation (XC) potential is discussed in context of optoelectronic properties. The changes in bandgap are attributed to the lifting of electronic degeneracy either by spin‐orbit coupling or symmetry lowering in rhombohedral distortion. The rhombohedral CsGeI3 is thus further emphasized to account its ferroelectricity with computed total polarization () around 32.75 μC cm−2. The suitable (1.45 eV), high absorption (≈105 cm−1), tolerable reflectivity (19%), and carrier effective masses (0.61 and 0.27) enable rhombohedral CsGeI3 (superior 30.5% spectroscopy‐limited maximum efficiency [SLME] at 1 μm thickness) to outperform conventional CsPbI3 (27.6% SLME at 1 μm) and others which may attract PV community to further address its underexplored promise.

Short-range disorder mediated stability of Zn in rock-salt MgO beyond configurational entropy

In rock-salt Mg0.50TM0.25Zn0.25O, CuO is more effective in stabilizing rock-salt ZnO in MgO, compared to CoO and NiO. Cu incorporation creates a wide metal–oxygen bond length distribution and short-range disorder and enhances Zn stabilization.

Unveiling the structure of calcium borate glass by neutron diffraction, MAS-NMR, Raman and first-principles calculations

Calcium borate glass is a challenging system, due to the rich variety of borate units and alterable boron coordination number, and hence they are also of particular interest for academic study. In this study, neutron diffraction, solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR) and Raman spectroscopy were combined with first-principles calculations, experience potential structure refinement (EPSR) simulations to investigate the structure of xCaO·(1-x)11B2O3 glass. Property data such as density and glass transition temperature were also measured to study the impact of structural changes on the properties of glasses. The structure of calcium borate glass was analyzed using various methods including structural unit, atomic pair bond length, coordination number, ring structure, chain structure and cavity distribution. Most notably, the atomic labeling method plays a key role in the structural analysis process. Through this method some new conclusions were obtained. For example, the increase of CaO content mainly leads to the conversion of BO to NBO in the glass structure, and has little effect on the content of BO3 and BØ4-. This result further leads to an increase in Ca-NBO interactions. Interestingly, the bond length distribution of Ca-NBO and B-NBO is shorter than that of Ca-BO and B-BO, so the glass structure becomes denser. The structural reason why the density of calcium borate glass is less than the crystal density was also revealed. This study contributes to unveiling the structure of calcium borate glass and exploring the correlation between the structure and properties of calcium borate glass, which provides a valuable reference for developing more valuable amorphous materials.

Structure and properties of graphullerene: a semiconducting two-dimensional C60 crystal

Graphullerene is a recently discovered, two-dimensional allotrope of carbon formed from C60 molecules. It has been synthesized in the form (C60Mg4)n and subsequently transformed into (C60)n by removal of the Mg atoms. Ab initio calculations are employed to examine the structure and properties of this material. Structurally, graphullerene is composed of strained C60 molecules. Each of these molecules is connected to six neighbors in a hexagonal network with a total of eight chemical bonds. We find this structure to be meta-stable, owing to the strain produced by the covalent bonding of the molecules. However, the inclusion of Mg atoms transforms the cohesion energy from negative to positive values by forming additional C-Mg bonds, creating an energetically stable material. In the absence of Mg, this allotrope is a pure carbon semiconductor with an indirect band gap. Phonon spectrum calculations confirm the dynamical stability of the material and yield its in- and out-of-plane sound velocities. In addition, symmetry breaking of the C60 molecules results in a distribution of bond lengths and creates vibrational modes that serve as a signature of graphullerene.

Relativistic DFT Calculations of Cadmium and Selenium Solid-State NMR Spectra of CdSe Nanocrystal Surfaces.

Solid-state NMR spectra have been used to probe the structure of CdSe nanocrystals and propose detailed models of their surface structures. Density functional theory (DFT)-optimized cluster models that represent probable molecular structures of carboxylate-coordinated surface sites have been proposed. However, to the best of our knowledge, 113Cd and 77Se chemical shifts have not been calculated for these surface models. We performed relativistic DFT calculations of cadmium and selenium magnetic shielding tensors on model compounds with previously measured solid-state NMR spectra with (i) the four-component Dirac-Kohn-Sham (DKS) Hamiltonian and (ii) the scalar and (iii) spin-orbit levels within the ZORA Hamiltonian. Molecular clusters with Cd and Se sites in varying bonding environments were used to model CdSe (100) and CdSe(111) surfaces capped with carboxylic acid ligands. Our calculations identify the observed 113Cd isotropic chemical shifts δ(iso) of -465, -318, and -146 ppm arising from CdSeO3, CdSe2O2, and CdSe3O surface groups, respectively, with very good agreement with experimental measurements. The 113Cd chemical shifts linearly decrease with the number of O-neighbors. The calculated spans (δ11 - δ33) encompass the experimental values for CdSe3O and CdSe2O2 clusters but are slightly larger than the measured value for CdSeO3 clusters. Relativistic DFT calculations predicted a one-bond 113Cd-77Se scalar coupling of 258 Hz, which is in good agreement with the experimental values of 250 Hz. With a dense coverage of carboxylic acid ligands, the CdSe (100) surface shows a distribution of Cd-Se bond lengths and J-couplings. Relativistic DFT simulations thus aid in interpretation of NMR spectra of CdSe nanocrystals and related nanomaterials.

COMPUTATIONAL MODELLING OF THE ACTIVATION PARAMETERS OF DIELS ALDER REACTION OF QUINOFLAVONOID AND 2, 3 DIMETHYLBUTA-1, 3-DIENE

Kinetics and thermodynamics of Diels alder reaction of quinoflavoniod and 2, 3 dimethylbuta-1,3-diene was studied using ab-initio method with Hartree Fock at 6-311G* basis set in spartan, Conformational search was carried out on the molecules to obtain the structures that has the lowest energy, an indication of the stability of the structure. Reaction path calculation was done on the most stable structure using C26 – C15 and C27 – C14 as reaction coordinate in 20 iterations, this was done to ascertain the reaction mechanism. Geometric calculation was carried out on the structures of the reactant, transition state and products to obtain the bond length, bond angle, dihedral angle and atomic charge distributions. Kinetics and thermodynamic parameters was calculated at 3480C. The reaction proceeded through a concerted asynchronous six-membered cyclic transition state. True saddle point was characterized and verified by the presence of only one imaginary vibrational frequency which smoothly connect the reactant, the transition state and the product. Negative values obtained for ?H* (-66.65kJ/mol shows that the reaction is exothermic and according to literature this may be as a result of conversion of two of the ?-bonds to two new ?-bonds). Values obtained for energy of formation (-1329.974 hatrees, -1329.911 hatrees, and 1330.023 hatrees for GS, TS and PRD respectively) according to Hammond’s postulate, confirms the exothermicity of the reaction. ?Greaction (-60.16kJ/mol, shows that the reaction is favourable, Negative ?S* (-11.29J/mol.K) suggests the spontaneity of the reaction and Ea (-63.76kJ/mol) suggests that the reaction involves transfer of electrons. It was also observed that rate constants decrease with increase in temperature, although very uncommon but suggested a complex reaction mechanism.

Analysis of surface stability of ferrocolumbite from combined DFT – Wulff construction simulations

Ferrocolumbite, a variegated oxide mineral bearing the strategic element niobium, exhibits an array of surface chemical compositions across various cleavage orientations. The complexity of Nb-bearing ores hinders the efficiency of separation processes, necessitating fundamental research to bridge the knowledge gap regarding the surface dominance and properties of the mineral. In this regard, density functional theory (DFT) simulations were performed to determine the stability of different low Miller index surfaces of ferrocolumbite. The thermodynamic Wulff construction theory was then employed to predict the morphology of a ferrocolumbite nanoparticle, taking into account the DFT-calculated surface energies and the symmetries in the ferrocolumbite crystal. Several descriptors, such as ionic atom density and bond length distribution, were partially successful in correlating with surface energies; however, no global correlation could be captured for this complex system. Our findings suggested oxygen-terminated surfaces generally exhibit greater stability than metal or mixed-metal–oxygen-terminated surfaces within a given facet. Based on the Wulff shape prediction, the {110}, {001}, {111}, and {021} facets contribute to >85% of the surface area of the ferrocolumbite particles after comminution. Therefore, a sound conclusion about the adsorption behavior of reagents on ferrocolumbite should include all of these facets. This fundamental research highlights the complex and diverse nature of the ferrocolumbite surface and paves the way for future investigations.

Predicting scale-dependent chromatin polymer properties from systematic coarse-graining

Simulating chromatin is crucial for predicting genome organization and dynamics. Although coarse-grained bead-spring polymer models are commonly used to describe chromatin, the relevant bead dimensions, elastic properties, and the nature of inter-bead potentials are unknown. Using nucleosome-resolution contact probability (Micro-C) data, we systematically coarse-grain chromatin and predict quantities essential for polymer representation of chromatin. We compute size distributions of chromatin beads for different coarse-graining scales, quantify fluctuations and distributions of bond lengths between neighboring regions, and derive effective spring constant values. Unlike the prevalent notion, our findings argue that coarse-grained chromatin beads must be considered as soft particles that can overlap, and we derive an effective inter-bead soft potential and quantify an overlap parameter. We also compute angle distributions giving insights into intrinsic folding and local bendability of chromatin. While the nucleosome-linker DNA bond angle naturally emerges from our work, we show two populations of local structural states. The bead sizes, bond lengths, and bond angles show different mean behavior at Topologically Associating Domain (TAD) boundaries and TAD interiors. We integrate our findings into a coarse-grained polymer model and provide quantitative estimates of all model parameters, which can serve as a foundational basis for all future coarse-grained chromatin simulations.

Metallic Germanium (111) Slab Structures.

Prior research has indicated that the surface electron conductivity of Ge (111) wafers surpasses that of Ge (100) and Ge (110) wafers. This disparity has been ascribed to the variations in bond length, geometry, and frontier orbital electron energy distribution across different surface planes. The ab initio molecular dynamics (AIMD) simulation is used for the thermal stability of the Ge (111) slabs with different thicknesses and has provided new knowledge of its potential applications. To delve deeper into the properties of Ge (111) surfaces, we executed calculations for one- and two-layer Ge (111) surface slabs. The electrical conductivities of these slabs at room temperature were determined to be 966081.89 and 760157.03 Ω-1 m-1, respectively, with a unit cell conductivity of 1.96 Ω-1 m-1. These findings align with actual experimental data. Notably, the electrical conductivity of the single-layer Ge (111) surface exceeded that of intrinsic Ge by 100,000 times, heralding intriguing potential for including Ge surfaces in future device applications.

On correlations between local chemistry, distortions and kinetics in high entropy nitrides: An ab initio study

High entropy alloys (HEAs) have triggered significant scientific interest due to their unusual structural stability combined with excellent mechanical and other functional properties. Recently, the high-entropy concept has also been applied to the field of protective coatings. We use ab initio calculations to provide an unbiased insight into their behavior at the atomic level. Namely, we focus on the interplay between high entropy (chemical complexity), sluggish diffusion, and (local) lattice distortions in the example of high configurational entropy sublattice nitride (HESN) ceramics. We show that the high entropy itself is not a guarantee for the sluggishness of diffusion (as quantified by migration barriers). Next, we propose a relation between the local distortions (measured by the width of lattice bond length distributions) and activation energies. The presented results provide examples that the core effects, characterizing the exceptional properties of HEAs, are system-specific and hence highlight the need for analyzing each system of interest individually.

Structural transformation and micro-phase separation of CaO-P2O5-SiO2 system under compression

This study investigated the pressure-induced structural transformation and micro-phase separation of the CaO-P2O5-SiO2 system at 3000 K and in the pressure range of 0–100 GPa based on molecular dynamics simulations. The structural characteristics were investigated based on the short range order, intermediate range order, and glassy network structure. The evolution of the local environment of network-forming ions (P5+, Si4+) and clustering behavior of network modifiers (Ca2+ ions) were clarified based on the radial distribution function, coordination number, and O-(P, Si, Ca) linkage distribution. The topologies of TOx (T = Si, P; x = 4, 5, 6) polyhedra were determined using the bond angle and bond length distribution. The linkages among TOx polyhedra, Ca2+ ion distribution, compositional and structural heterogeneities, micro-phase separation, and mechanism of Ca2+ incorporation into glassy networks were also visually analyzed and investigated in detail.

Molecular Dynamic Simulations and Experiments Study on the Mechanical Properties of HTPE/PEG Interpenetrating Polymer Network (IPN) Binders.

The mechanical properties of HTPE/PEG interpenetrating polymer network (IPN) binders were systemically studied with molecular dynamics (MDs) simulations and experiments. In this study, an algorithm was used to construct the crosslinking interpenetrating polymer network models and then the mechanical behaviors of Hydroxyl-terminated polyethylene glycol-tetrahydrofuran co-polyether/poly ethylene glycol (HTPE/PEG) IPN models were analyzed at a molecular scale. Firstly, glass transition temperatures (Tg), mean square displacement (MSD) and mechanical properties of IPN crosslinked model simulations showed that better thermomechanical parameters appeared at low temperatures, which were in good agreement with the experimental methods, including dynamic mechanical analysis and uniaxial tensile. Then bond-length distribution was performed to verify the crosslinked structures between prepolymers and curing agents. FTIR-ATR spectra analysis of four IPN binder specimens also gave a convictive result to the special interpenetrating polymer network of polyether polyurethane binders. Cohesive energy density and friction-free volume explained how the micro-structures of IPN crosslinked models and the force of inter-molecule chains affected the mechanical behaviors of the HTPE/PEG polyurethane matrix. Lastly, the morphology of IPN binder specimen tensile fracture indicated the mechanism at different temperatures. These studies were helpful in understanding the mechanical properties of HTPE/PEG interpenetrating polymer network binders and provide molecular insight into mechanisms of mechanical behaviors, which would guide the property improvement of HTPE propellant.

Comparison of the different distribution functions in Gd-doped ceria system by molecular dynamics simulations

Cerium dioxide-based materials are among the most studied for applications in the energy and environmental fields and are also of interest in biology and medicine. The fluorite structure of CeO2 is locally distorted by the concomitant presence of doping cations, such as Gd3+ and oxygen vacancies. The cation-anion bond length distribution then becomes increasingly asymmetric with the doping ratio and temperature. In these cases, the MD simulation results indicate that the commonly used maximum of the pair correlation function g(r) first peak can no longer be adopted to estimate the mean bond length. To determine the true cation-anion bond length, the analysis of the radial distribution function R(r) first peak is necessary. Furthermore, the asymmetry of this peak must be accounted for when extracting the mean value of the distribution. The gap between the g(r) maximum and the R(r) mean position derived from the fit using a skewed Gaussian function clearly increases with the doping ratio and temperature, leading to different conclusions concerning bond length evolution. The present study also suggests that care must be taken when the bond length is deduced from the pair distribution functions G pdf(r) as is the case in total scattering experiments (x-ray and neutrons). Finally, relations between the cumulants of the effective distribution of distances as determined in extended x-ray absorption fine structure experiments and the cumulants describing the real distance distribution are proposed considering that both these distributions are modelled by a skewed Gaussian function.

Co-crystals of polynuclear aromatic hydrocarbons and 9H-carbazole with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone acceptor: Varieties in crystal packing, Hirshfeld surface analysis and quantum-chemical studies

Co-crystals formed by polynuclear aromatic hydrocarbons (PAH) chrysene, benz(a)anthracene, triphenylene(9,10-benzophenanthrene), benzo(a)pyrene, dibenz[a,c]anthracene, and 9H-carbazole as π-electron-donor (D) molecules, with π-electron acceptor, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) were synthesized, and their crystal structures were determined using single-crystal X-ray diffraction analysis. All co-crystals exhibit 1:1 donor / acceptor ratio and adopt mixed-stacking motifs. The donor(D)-acceptor (DDQ) π-π interactions in stacks are complemented by different sets of D…D, D…DDQ and DDQ…DDQ intermolecular interactions between stacks whose diversity originates from different degree of D/DDQ mismatch and manifests in dissimilar crystal packing motifs. The parallel face-to-face stacking was registered in chrysene-DDQ, while benz(a)anthracene-DDQ reveals brickwork crystal packing with significant parallel slippage. The rest four co-crystals show fairly different herringbone-type crystal packing with rearrangement of intermolecular interactions. The distribution of intermolecular contacts and impact of π-π interactions were evaluated through Hirshfeld surface analysis. Molecular orbital energies as well as bandgaps were calculated using DFT. Degree of charge-transfer was estimated based on bond length distribution in the acceptor molecule for each of the co-crystals.

Corrosive Influence of Carbon Dioxide on Crack Initiation in Quartz: Comparison With Liquid Water and Vacuum Environments

AbstractThe stimulation of crack growth in quartz and siliceous materials by injecting carbon dioxide (CO2) represents a key technology in long‐term carbon storage and in the development of natural gas wells. While this technology is widely used, the molecular impact of CO2 interactions on the solid matrix is only incompletely understood. In this work, we employ reactive molecular dynamics simulations to study how the CO2 fluid environment affects the mechanical properties of pre‐cracked single‐crystal quartz. The thermodynamic conditions of interest are those relevant to subsurface reservoirs. We report how structural properties of quartz—bond length distribution and crack tip shape—evolve upon introduction of a fluid. These properties are directly related to macroscopic quantities of the global stress–strain curves, thus reaffirming the inherent coupling across multiple scales for fluid–solid interactions in the subsurface. We find that CO2 reduces the fracture toughness of quartz by 12.1% compared to that of quartz in vacuum, thereby promoting crack growth and enhancing fluid transport in the subsurface.

Experimental and molecular dynamic studies of phase transformation and amorphization in silicon during high-energy ball milling

Nano-sized and amorphous silicon (α-Si) have a wide range of properties and applications, but their atomistic structure and the process of crystal evolution are still unclear. In this study, a combined action is used to present a mechanism for the crystal-to-amorphous solid–solid phase transition in silicon during mechanical alloying (MA) at room temperature. For this purpose, the ball milling of silicon was performed and changes in crystallographic structure and amorphous phase were studied by scanning electron microscopy (SEM), X-ray diffraction patterns (XRD), and energy dispersive X-ray spectroscopy (EDX). The process of changing phase was determined by quantitative phase analysis (MAUD/Rietveld refinement). In the simulation part, a crystal structure of silicon consisting of 64 atoms was created and uniaxial and biaxial external pressures were applied randomly by BIOVIA Materials Studio. The time step and simulation time were 1 and 300 Ps, respectively. Important atomic properties including density, mean square displacement (MSD), angle length and bonds distribution, and the fraction of broken bands were measured after applying per compression. Atomic structure and changes in crystalline phase to nano and amorphous phases were studied and these results had a considerable agreement with the experimental part and well-known previous studies. The diamond cubic structure shows a remarkable toughness during the modeling and so amorphization was performed at an exponential evolution. The Results of the simulations showed that the bond angle and length distribution and MSD, were increased significantly, and in contrast, density was decreased to 1.254 g/cm3. The percentage of the broken Si-Si bonds was 58.12 % and a new definition of Si amorphization based on the fraction of covalent bonds was proposed. The amorphization started from the surface of Si and spread by the partial distribution toward the crystal structure. These findings show that the proposed mechanism based on the fraction of breaking bonds and pressure-induced amorphization could be used for the accurate simulation of the solid–solid phase transformation.