Abstract Ab Initio Molecular Dynamics Research Articles

Boron Incorporation in Silicate Melt: Pressure-induced Coordination Changes and Implications for B Isotope Fractionation

Ab initio molecular dynamics simulations have been employed to investigate the nature of boron incorporation in a haplobasalt melt at pressures up to 8 GPa. At ambient pressure, boron is predominantly incorporated as trigonal planar BO3 units. With increasing pressure, the proportion of tetrahedral BO4 increases markedly in parallel with increases in the coordination of other cations in silicate liquids. In contrast to studies of high-pressure boron-rich silicate glasses and liquids where boron units are polymerized, simulations of low B-concentration liquid here indicate that boron does not adopt a significant role as a network-forming cation. Marked changes in the proportion of BO4 in silicate melt at even moderate pressures (from 5 to 20%, over the pressure range 0–3 GPa) imply that pressure may significantly affect the extent of melt/fluid and melt/crystal boron isotope fractionation. This pressure-effect should be considered when using boron isotope data to elucidate processes occurring within the mantle.

Dynamical and structural properties of adsorbed water molecules at the TiO2 rutile-(110) surface: interfacial hydrogen bonding probed by ab-initio molecular dynamics

ABSTRACT Ab-initio molecular dynamics (AIMD) simulations have been carried out to study a range of different and energetically-accessible adsorbed-water configurations and motifs for their vibrational and structural characteristics, in contact with rutile-(110) interfaces at 100 K. The radial pair distribution function between the titanium atoms at the interface and the hydrogen and oxygen atoms in the water monolayer show an orientation of the water molecules parallel to the surface of titania, and with hydrogen atoms pointed in the opposite direction to the surface. In some cases, a distinctive vibrational frequency region between 2500 and 3000 cm−1 has also been observed, due to a strong dispersion interaction between water molecules. This behaviour is also seen in experimental studies of thin-film water coverage on TiO2 surfaces.

Maleimide: a potential building block for the design of proton exchange membranes studied by ab initio molecular dynamics simulations

Ab initio molecular dynamics (AIMD) simulations are applied to the study of proton transport in solid state maleimide.

Structural and electrical behaviour in Bi14YO22.5

Ab initio molecular dynamics calculations show low energy barriers for oxide ion conduction along c-axis channels in βIII-Bi14YO22.5.

Correlated ab initio molecular dynamics simulations of the acetone–carbon dioxide complex: implications for solubility in supercritical CO2

Ab initio molecular dynamics simulations of the acetone–CO2 complex (MP2/6-31G(d) level) were performed to investigate the effect of dynamics at finite temperature on the weak electron donor–acceptor intermolecular interactions. In addition, we carried out a study of the free energy of formation of the complex by means of umbrella sampling technique at the MP2 level with a perturbative CCSD(T) correction. The potential of mean force was obtained along a reaction coordinate describing the acetone–CO2 interaction. The results obtained here support some hypothesis that we already explored in past works using static electronic calculations. In particular, when interacting with a molecule having a carbonyl function, carbon dioxide displays both Lewis acid and Lewis base behaviour. This property can be exploited to design molecular systems that are easily solubilised in supercritical CO2.

Elastic Properties of CaSiO3 Perovskite from ab initio Molecular Dynamics

Ab initio molecular dynamics simulations were performed to investigate the elasticity of cubic CaSiO3 perovskite at high pressure and temperature. All three independent elastic constants for cubic CaSiO3 perovskite, C11, C12, and C44, were calculated from the computation of stress generated by small strains. The elastic constants were used to estimate the moduli and seismic wave velocities at the high pressure and high temperature characteristic of the Earth’s interior. The dependence of temperature for sound wave velocities decreased as the pressure increased. There was little difference between the estimated compressional sound wave velocity (VP) in cubic CaSiO3 perovskite and that in the Earth’s mantle, determined by seismological data. By contrast, a significant difference between the estimated shear sound wave velocity (VS) and that in the Earth’s mantle was confirmed. The elastic properties of cubic CaSiO3 perovskite cannot explain the properties of the Earth’s lower mantle, indicating that the cubic CaSiO3 perovskite phase is a minor mineral in the Earth’s lower mantle.

Ab-initio molecular dynamics simulation of δ-Bi3YO6

Abstract Ab-initio molecular dynamics (MD) study of oxygen ion diffusion in the oxide ion conducting solid electrolyte δ-Bi3YO6 is presented. Vacancy ordering models were tested by structure relaxation and that for vacancy pairs was found to have the highest total energy per atom, while those for , and random vacancy distributions were found to have similar energies. Evidence for polarization of bismuth charge density is seen for and vacancy pair configurations, consistent with stereochemical activity of the Bi 6s2 lone pair. MD studies of oxygen diffusion were carried out at three temperatures. Vacancy pair alignments during these simulations were predominantly in the direction, consistent with previous neutron total scattering results.

Local structure of Co55Ta10B35 amorphous alloy investigated by ab-initio molecular dynamics

Ab-initio molecular dynamics simulation was performed to investigate the local atomic structure of Co55Ta10B35 alloys. Pair distribution function, coordination number, HA index and Voronoi polyhedra were used to describe the detailed local structure of this alloy. It was revealed Co7Ta1B2, Co6Ta1B2 and Co8Ta2B4 among the dominant 〈0 3 6 0〉, 〈0 4 4 0〉, 〈0 1 10 2〉 and 〈0 3 6 4〉 polyhedra were the basic local structure units in Co55Ta10B35 amorphous alloy. Furthermore, most of the dominant polyhedra tended to have Ta atoms involved and these polyhedra may have a critical role during glass formation.

Structure Simulation Calculation of Impurities B with Fe, Al or Ca in Metallurgical Grade Silicon

Ab initio molecular dynamics (MD) calculations had been performed in this work to simulate the interactions of B with Fe, Al or Ca in metallurgical-grade silicon (MG-Si). The temperature of the MD simulations is 0K, the simulation time is 1ps. All the calculations were performed by using the CASTEP module of Materials Studio 4.3 software package. The geometry optimizations of impurities B with Fe, Al and Ca in MG-Si were performed with density functional theory (DFT) calculation. The Density of States of the optimized structures was calculated and the results have the potential application in guiding the boron removal from MG-Si by acid leaching.

AB INITIOMOLECULAR DYNAMICS SIMULATIONS ON LOCAL STRUCTURE AND ELECTRONIC PROPERTIES IN LIQUIDSbFROM 913 K TO 1193 K

Ab initio molecular dynamics simulations on liquid Sb have been carried out at five different temperatures from 913 K to 1193 K. We have investigated the temperature dependence of structure properties including structural factor S(Q), pair correlation function g(r), bond-angle distribution function g3(θ), cluster properties and bond order parameter Q4and Q6. A shoulder was reproduced in the high wave number side of the first peak in the S(Q) implying that the residual structure units of crystalline Sb remain in liquid Sb . There is a noticeable bend at around 1023 K in the temperature dependence of the first-peak height of S(Q), the cluster properties and bond order parameter Q4, respectively, indicating that an abnormal structural change may occur at 973–1023 K.

Study of the stability of aluminium trimeric clusters in aqueous solutions

Ab initio molecular dynamics (AIMD) based on density functional theory has been used to study small aluminium–oxygen complexes in water. Such Al–O clusters have been seen in several recent mass spectrometry studies. In this study, we have focused on trimeric Al–O clusters. The initial very compact trimeric Al–O structures opened up and formed linear Al–O chains. The typical Al–O coordination number in these chain structures was 5. We have performed long (up to 200 ps) AIMD simulations and these chain structures are stable on the nanosecond time scale. We have also studied the reactivity of the Al–O dimer and solvated Al. We found a formation path for the trimeric cluster, which has a action barrier (0.04 eV) and a reaction free energy of − 0.55 eV. This suggests that the association of a dimer and a monomer Al–O species is fast and thermodynamically a very favourable process.

A First-Principles Study on Water Flow Through Single-Walled Carbon Nanotubes Using Artificial Neural Network Method

Ab initio molecular dynamics simulations are done to elucidate the electronic structure and properties of water/single-walled carbon nanotubes (SWCNTs) systems. The artificial neural network (ANN) approach and statistical methods are then used to model and analyze these properties. The ANN method substantially speeds up the ab initio electronic structure calculations and has superior accuracy in mimicking the results of such calculations. We aim to understand the effects of CNT chirality, temperature, and CNT flexibility on the water diffusion inside SWCNTs. In this regard, the CNT is fixed implies that the position of CNT is kept constant during the diffusion process. Statistical analysis of results shows that there is a nonmonotonic variation of diffusion length of water with respect to the CNT chirality. However, an increase in temperature and rigid CNTs accelerate the water diffusion.

The influence of the lone electron pair on structure and dynamics of divalent group IV metal ion hydrates

Ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulations have provided details on the varying influence of the lone electron pair on the structure and dynamics of Ge(II), Sn(II) and Pb(II) ions in aqueous solution. Ge(II) and Sn(II) hydrates are highly unsymmetric, forming strongly and weakly coordinated hemispheres. In the case of Pb(II), the effects can be seen upon comparison with the divalent Hg(II) ion which has no lone pair. This work shows the capability of QMCF MD in obtaining details of solvate complexes difficult to study by experimental techniques.

Ab Initio Simulations of Low-K and Ultra Low-K Dielectric Interconnects

Ab initio molecular dynamics simulations were carried out to study low-k/ultra low-k dielectric systems comprising Cu/Ta/SiLK-like polymer. A study of the motion of single metal atoms of Cu and Ta in the SiLK-like polymer showed that Cu atom motions are effected by jumps between cavities inside the polymer and that Ta is more sluggish than Cu not only because of its larger mass but also because of stronger affinity to the polymer. It was also found that crosslinking of the polymer did not affect the motion of the metal atoms. Simulations of deposition showed that a thin Ta diffusion barrier does not have good structural integrity to prevent Cu-diffusion when directly deposited onto the SiLK; the barrier performance was greatly improved after introducing a Si-based film between the Ta and SiLK.

Ab initio MD simulations of a prototype of methyl chloride hydrolysis with explicit consideration of three water molecules: a comparison of MD trajectories with the IRC path

Ab initio molecular dynamics simulations at the Hartree-Fock/6-31G level of theory are performed on methyl chloride hydrolysis with explicit consideration of one solute and two solvent water molecules at a temperature of 298 K. The reaction involves the formation of a reactant complex and the energy surface to the transition state is found to be simple. Two types of trajectories toward the product are observed. In the first type, the system reaches an intermediate complex (complex-P1) region after two nearly concerted proton transfers involving the attacking water molecule and the solvent water molecules. These trajectories resemble the intrinsic reaction coordinate trajectory. The thermal motion of the atoms leads the system to another intermediate complex (complex-P2) region. A second type of trajectory is found in which the system reaches the complex-P2 region directly after the proton transfers. In both of these forward trajectories, back proton transfers lead the system to a final complex-F region which resembles protonated methanol.

Ab initiomolecular dynamics study of metallocene catalysed ethylene polymerization

Ab initio molecular dynamics simulations of a catalytic reaction are presented. Ethylene insertion is observed to proceed in a SiH2-bridged di-(cyclopentadienyl)methylzirconocene cation as well as in the corresponding titanocene cation. The entire reaction path starting from the π coordinated ethylene-metallocene complex up to and including propyl formation takes place in about 150 fs for the zirconocene and 500 fs for the titanocene. For both a Zr and a Ti based monocyclopentadienyl metallocene no insertion was observed, which is indicative of a barrier to insertion. In accordance with this, stepwise variation of the relevant C-C distance along the reaction path as set prior to the dynamics simulation did reveal insertion. These data are in qualitative agreement with results obtained from static simulations on similar species.