Tight-binding Molecular Dynamics Study Research Articles

Density-functional tight-binding molecular dynamics study on fixation reaction of CO2 to styrene oxide catalyzed by Mg-MOF-74 metal-organic framework

Abstract Carbon capture and utilization is a strategy to reduce CO2 emissions by utilizing them to synthesize fine chemicals. Mg-MOF-74 exhibits exceptional CO2 adsorption capacity and functions as a catalyst in styrene carbonate synthesis from CO2 and styrene oxide. We examined the structural properties and energetics of styrene carbonate synthesis in Mg-MOF-74 at the third-order density-functional tight-binding level. A novel reaction mechanism via the formation of a seven-membered ring intermediate was found to exhibit a lower Gibbs activation energy than the previously proposed mechanism.

Transport properties of Ag decorated zigzag graphene nanoribbons as a function of temperature: a density functional based tight binding molecular dynamics study

The systemic study of the electronic transport (ET) properties of transition metal (TM) functionalized graphene was done with the aid of self-consistent charge density functional based tight binding (DFTB) method. Results show that among the TM considered, Silver metal adsorbed in the surface of graphene and its lower dimensional analogue zigzag graphene nanoribbon (ZGNR) can open its gapless bandstructure. This can be attributed to the breaking of bond and inversion symmetry. Further, the inherent effect of phonons (lattice vibrations) on the transport properties Ag-adsorbed ZGNR were investigated based on DFTB molecular dynamics (MD) simulation. Results show that excellent ET properties can be attributed to the Ag and ZGNR interaction. In addition, due to the unceasing lattice vibration of the Ag/ZGNR, the ET changes. Knowledge about the quantum of vibration at temperature T is quite important to elucidate its role governing the resulting ET. As the phonon having shorter wave length significantly increases at elevated temperatures, the corresponding forward bias voltage across the Ag/ZGNR increases. There is an increase in the conductance of vibrating Ag/ZGNR at elevated temperatures. A single-gated field effect transistor based on Ag-adsorbed ZGNR can act as a potential semiconductor for modern electronic applications.

Solubility of aminotriethylene glycol functionalized single wall carbon nanotubes: A density functional based tight binding molecular dynamics study.

Pristine CNTs are exemplary hydrophobic solutes; properly functionalized CNTs can be seen as hydrophilic ones. The solubility of aminotriethylene glycol (ATG) functionalized single walled carbon nanotubes (fSWCNTs) were examined using density functional based tight binding method. According to the dynamics study, the ATG-fSWCNTs interaction energies (IE) and diffusion coefficients (D) are diameter dependent. As the diameter of the (n,0) tube is incrementally increased, a distinguishable pattern is observed, specifically the IE of the ATG-fSWCNT in water is quite higher for n that is an integral multiple of three (n = 9,12,15) while the D is lower due to its π bonding structures. In general, the metallic ATG functionalized nanotube possess a higher IE and a much lower D in aqueous media. © 2019 Wiley Periodicals, Inc.

Small transition metal cluster adsorbed on graphene and graphene nanoribbons: A density functional based tight binding molecular dynamics study

Abstract The systemic study of the electronic properties of different transition metals (TMs-Sc, Ti, Fe, Co, Ni, Zn, Ag and Au) adsorbed in the surface of graphene was done with the aid of self-consistent charge density functional based tight binding method. Results show that the Silver metal adsorbed in the surface of graphene can open its gapless bandstructure. In addition, a single-gated field effect transistor based on Ag-adsorbed on zigzag graphene nanoribbon (zGNR) can act as a potential semiconductor for modern electronic applications. An important feature is that the Ag does not break the structure of zGNR on adsorption. Further, the resulting Ag/zGNR energy band gap is inversely proportional on the dimer lines across its width as predicted by tight-binding calculations.

Hydrogen adsorption of Ti-decorated boron nitride nanotube: a density functional based tight binding molecular dynamics study

The hydrogen adsorption capabilities of Titanium functionalized single-walled BN nanotubes (BNNTs) with B–N defects was assessed by density-functional theory tight binding (DFTB) method. According to the DFTB molecular dynamics simulations, the BNNT structures were thermodynamically stable, the Ti atom once incorporated with the B–N defects present in BNNT (Ti–BNNT) protrudes to the external surface of the BNNT sidewall. The titanium atoms does not agglomerate to form any metal clusters. The results revealed that at 77 K and 10,000 KPa, the H2–Ti–BNNT has a gravimetric hydrogen storage capacity above 7 wt% ideal for department of energy specifications. Further calculations suggest that the Ti–BNNT has a good affinity towards H2 molecules and under low pressure of 500 KPa. The H2 stays close to the Ti metal due to its partially cationic character with some H2 attaching itself at the BNNT surface due to heteropolar bonding. H2 atoms is physisorbed in analogous to or resembling something molecular near the Ti sites which gives rise to a significant storage capacity for H2 in these modified BNNT.

A tight-binding molecular dynamics study of the noble metals Cu, Ag and Au

We have used the Naval Research Lab (NRL) tight-binding (TB) method to study the electronic and mechanical properties of the noble metals. In order to perform molecular dynamics simulations, we used new TB parameters that work well at smaller interatomic distances. The TB parameters were fitted to the fcc, bcc and sc periodic structures and were demonstrated to be transferable and robust for calculating additional dynamical properties which they had not been fitted to. We calculated the phonon frequencies and density of states at finite temperature and we also performed simulations to determine the temperature dependence of the coefficient of thermal expansion and the mean squared displacement. The energy for vacancy formation as well as energy for fcc-based, bcc-based clusters and icosahedral clusters of different sizes were also calculated. The results compared very well with experimental observations and independent (non-fitted) first-principles density functional calculations.

Divide-and-Conquer Density-Functional Tight-Binding Molecular Dynamics Study on the Formation of Carbamate Ions during CO2 Chemical Absorption in Aqueous Amine Solution

Divide-and-Conquer Density-Functional Tight-Binding Molecular Dynamics Study on the Formation of Carbamate Ions during CO2 Chemical Absorption in Aqueous Amine Solution

Tight-Binding Quantum Chemical Molecular Dynamics Study on the Friction and Wear Processes of Diamond-Like Carbon Coatings: Effect of Tensile Stress.

Diamond-like carbon (DLC) coatings have attracted much attention as an excellent solid lubricant due to their low-friction properties. However, wear is still a problem for the durability of DLC coatings. Tensile stress on the surface of DLC coatings has an important effect on the wear behavior during friction. To improve the tribological properties of DLC coatings, we investigate the friction process and wear mechanism under various tensile stresses by using our tight-binding quantum chemical molecular dynamics method. We observe the formation of C-C bonds between two DLC substrates under high tensile stress during friction, leading to a high friction coefficient. Furthermore, under high tensile stress, C-C bond dissociation in the DLC substrates is observed during friction, indicating the atomic-level wear. These dissociations of C-C bonds are caused by the transfer of surface hydrogen atoms during friction. This work provides atomic-scale insights into the friction process and the wear mechanism of DLC coatings during friction under tensile stress.

Divide-and-Conquer Density-Functional Tight-Binding Molecular Dynamics Study on the Formation of Carbamate Ions during CO2 Chemical Absorption in Aqueous Amine Solution

Abstract Divide-and-conquer-type density-functional tight-binding molecular dynamics simulations of the CO2 absorption process in monoethanolamine (MEA) solution have been performed for systems containing thousands of atoms. The formation of carbamate anions has been widely investigated for neutral systems via ab initio molecular dynamics simulations, yet the present study is aimed at identifying the role of hydroxide ions in acid-base equilibrium. The structural and electronic analyses reveal that the hydroxide ion approaches, via Grotthuss-type shuttling, the zwitterionic intermediates and abstracts a proton from the nitrogen atom of MEA. We also estimated the fraction of reacted CO2 and carbamate formed at different initial CO2 concentrations that confirm a high absorbed CO2 concentration decreases the fraction of MEA(C) formed due to the abundance of MEA(Z) in the solution.

High kinetic stability of hypercubane: Tight-binding molecular dynamics study

Using tight-binding molecular dynamics simulations we study thermal stability of the hypothetical hydrocarbon hypercube or tesseract which is called hypercubane over the wide temperature range T=1000⿿2000K. We find that hypercubane (in the case of its synthesis) will show high kinetic stability and its lifetime at room temperature will reach ⿼1014s. The molecular dynamics data obtained is confirmed by means of the additional PBE/6-311G(d,p) density functional calculations. Unique channel and final products of the hypercubane decay are also determined.

Growth mechanisms and selectivity for graphene or carbon nanotube formation on SiC ([formula omitted]): A density-functional tight-binding molecular dynamics study

We have performed density-functional tight-binding simulations mimicking the thermal decomposition of the SiC (0001¯) surface to reproduce the experimentally observed growth of either graphene or carbon nanotubes. A graphene-like network was obtained from a layer-by-layer decomposition of the SiC surface. The interaction between graphene and SiC was found to be relatively weak. Meanwhile, carbon nanotubes grew when a five-membered ring was initially formed together with a carbon chain. The simulation results suggest that growth selectivity depends on the overall carbon network connectivity and carbon aggregation speed at the very initial stage of the decomposition process.

Interaction between Atomic Vacancies in Crystalline Si Wafer: A Tight-binding Molecular Dynamics Study

Interaction between Atomic Vacancies in Crystalline Si Wafer: A Tight-binding Molecular Dynamics Study

Fate of methanol molecule sandwiched between hydrogen-terminated diamond-like carbon films by tribochemical reactions: tight-binding quantum chemical molecular dynamics study

Recently, much attention has been given to diamond-like carbon (DLC) as a solid-state lubricant, because it exhibits high resistance to wear, low friction and low abrasion. Experimentally it is reported that gas environments are very important for improving the tribological characteristics of DLC films. Recently one of the authors in the present paper, J.-M. Martin, experimentally observed that the low friction of DLC films is realized under alcohol environments. In the present paper, we aim to clarify the low-friction mechanism of the DLC films under methanol environments by using our tight-binding quantum chemical molecular dynamics method. We constructed the simulation model in which one methanol molecule is sandwiched between two hydrogen-terminated DLC films. Then, we performed sliding simulations of the DLC films. We observed the chemical reaction of the methanol molecule under sliding conditions. The methanol molecule decomposed and then OH-termination of the DLC was realized and the CH3 species was incorporated into the DLC film. We already reported that the OH-terminated DLC film is very effective to achieve good low-friction properties under high pressure conditions, compared to H-terminated DLC films. Here, we suggest that methanol environments are very effective to realize the OH-termination of DLC films which leads to the good low-friction properties.

On the thermal stability of tetrahedrane: Tight-binding molecular dynamics study

Tight-binding molecular dynamics simulations are carried out to analyze the thermal stability of the C 4H 4 tetrahedrane molecule over the wide temperature range T = 400–1000 K. The temperature dependence of the C 4H 4 lifetime τ to the decay moment is obtained. The deviation of τ( T) from the Arrhenius law is discussed. The height of the minimum energy barrier preventing the tetrahedrane decomposition is found to be 0.46 eV. Possible channels and final products of the tetrahedrane decay are determined.

Initial Stage of Consolidation of Silicon-Carbide Nanocrystals under Pressure: A Tight-Binding Molecular-Dynamics Study

Tight-binding molecular-dynamics (TBMDs) simulations are performed to study atomic and electronic structures during high-temperature consolidation processes of nanocrystalline silicon carbide under external pressure. We employ a linear-scaling method (the Fermi-operator expansion method) with a scalable parallel algorithm for efficient calculations of the long time-scale phenomena. The results show that microscopic processes of the consolidation depend strongly on initial orientations of the nanocrystals. It is observed that an orientational rearrangement of the nanocrystals initially misaligned is induced by an instantaneous shearing force between nanocrystals, whereas the aligned system undergoes densification without shearing. Analysis on an effective-charge distribution and an average bond-order distribution reveals electronic-structure evolutions during these processes.

Tight-binding molecular dynamics study of the hydrogen-induced structural modifications in tetrahedral amorphous carbon

A tight-binding molecular dynamics study of the structural evolution in tetrahedral amorphous carbon networks under dynamic hydrogen saturation is presented. The incorporation of hydrogen results in higher degrees of network disorder in second-neighbour distances, and initiates orbital re-hybridization that relaxes network stress. Using the simulated structures, numerical tests are performed to verify the effectiveness of a new structural order parameter for tetrahedrally-bonded solids. It is found that the island of accessible information, within the order parameter field shows a linear dependence between the fluctuations in first- and second-nearest-neighbour distances at a preferred orientation of 36°. A comparison with similar studies on hydrogenated amorphous silicon suggests that the local network structure of tetrahedrally-bonded amorphous solids obey the same ordering rule irrespective of differences in chemical species.

Environment-dependent Empirical Tight-binding Molecular Dynamics Study of Amorphous Silicon

A 216-atom computer model of amorphous silicon is generated by rapid quenching from the silicon melt using an environment-dependent empirical tight-binding (EDETB) potential model. The pair correlation function, the bond angle distribution, and the electronic density of states are in good agreement with available experimental data and ab-initio molecular dynamics results. The quenching rate appears to play an important role in the structures of the computer model. If possible, a quenching rate that approaches the experimental value should be used to build a more structurally reliable computer model.

Tight-binding molecular dynamics study of palladium

We present a study of palladium by the NRL tight-binding (TB) method. We constructed a set of TB parameters by fitting to first-principles data for the electronic energies of face-centered cubic (fcc) and body-centered cubic (bcc) Pd as a function of volume. This TB Hamiltonian was then used to calculate phonon frequencies and elastic constants. Our calculations show good agreement with experiments and demonstrate the efficiency of the NRL-TB scheme. In addition, we performed tight-binding molecular dynamics simulations to calculate the density of states, coefficient of thermal expansion, mean-squared displacement, and energy of vacancies formation at finite temperature.

From multilayered graphite flakes to nanostructures: A tight-binding molecular dynamics study

The nucleation of nanostructures from multilayered graphite flakes with different sizes has been studied by tight-binding molecular dynamics simulations. In agreement with the previous studies, double-layered graphite flakes can be curled up to form the classical carbon nanotubes of different diameters. More interestingly, in given conditions, the transformations from four or six layers of graphite flakes to nanotube bends, heterojunctions, and T or Y junctions have also been observed in the simulations. All of the corresponding results show a two-step dynamic process. This may be a possible mechanism for the nucleation of various carbon nanotube junctions. Additionally, by analyzing and comparing the nucleation processes, it is found that the interlayer distances of multilayered graphite flakes affect the structural transformations to heterojunctions, T or Y junctions.

Point defects in pure amorphous silicon and their role in structural relaxation: A tight-binding molecular-dynamics study

Structural relaxation in pure amorphous silicon a-Si produced by ion implantation has been attributed to the annihilation of point defects vacancies and interstitials introduced during the amorphization process. We have studied this problem by using tight-binding molecular-dynamics simulations. We find that structural defects can, indeed, be identified in a-Si— they manifest themselves through a strong correlation between the charge and the volume of nearby atoms. The relaxation of these defects proceeds via the recombination of the dangling bonds. This results in an increase in the coordination number at constant density; the relaxation of a-Si, therefore, results from local, rather than global, structural changes, in full agreement with the highprecision x-ray diffraction experiments of Laaziri et al. Phys. Rev. Lett. 82, 346