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Ab Initio Molecular Dynamics Simulation (ab + initio_molecular_dynamics_simulation)
Selected AbstractsAb Initio Molecular Dynamics Simulation of a Water,Hydrogen Fluoride Equimolar MixtureCHEMPHYSCHEM, Issue 1 2005Christian Simon Abstract Hydrogen fluoride and water can be mixed in any proportion. The resulting solutions have unique acidic properties. In particular, hydrogen fluoride undergoes a weak-to-strong acidity transition with increasing concentration of HF. To supplement the knowledge already obtained on dilute or moderately concentrated solutions and gas-phase aggregates, an equimolar mixture is studied here by Car,Parrinello molecular dynamics. The natures of the ions and of the complexes formed in the equimolar liquid were determined. Specifically, H3O+, H5O2+, FHOH2, and HF2,were spontaneously obtained while only hydronium and fluoride ions pre-exist in the equimolar crystal. The behaviour of the proton in the equimolar liquid was compared with mixtures of other proportions simulated previously in an attempt to relate proton dynamics to acidity. In the same way, the behaviour of HF2,was also examined. In this case, proton localization and transfer appeared to be driven by the fluctuating environment of the solvated ion. [source] Wavelet transform analysis of ab initio molecular dynamics simulation: Application to core-excitation dynamics of BF3JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2007Takao Otsuka Abstract We propose a novel analysis method of ab initio molecular dynamics (AIMD) simulation using a continuous wavelet transform (c-WT) technique. The c-WT technique, one of the time-frequency signal analysis methods, provides a clear view of the dynamical information in time developments. Combined with the auto-correlation function of velocity by AIMD simulation, c-WT analysis enables us to well understand dynamical distribution, such as the vibrational properties following a change of electronic structure in a molecular system. As a practical application, AIMD simulation of core-excited BF3 (B1s , 2a) is illustrated. AIMD simulation leads to the change of vibrational motion as well as structural deformation by core-excitation. The c-WT analysis clarifies the relationship between structural deformation and the related significant vibrational modes in core-excitation within 50 fs. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Disproving a Silicon Analog of an Alkyne with the Aid of Topological Analyses of the Electronic Structure and Ab Initio Molecular Dynamics CalculationsCHEMPHYSCHEM, Issue 9 2005Carlo A. Pignedoli Dr. Abstract A silicon compound has recently been synthesized that was claimed to exhibit the first realization of a silicon,silicon triple bond. We debate this classification on the basis of a thorough investigation of the nature of the chemical bond, using the rigorous topological analysis of the electron density as developed in Bader's atoms-in-molecules theory, that of the electron localization function and the related orbital-independent definitions of the bond order. Our results refer both to the ground-state geometry and to nonequilibrium configurations, which are accessed by the system in a room-temperature ab initio molecular dynamics simulation. We also use the reciprocal compliance force constant as an independent chemical descriptor. All the above procedures are in agreement and do not support the classification of the silicon,silicon central bond as triple. The characterization which consistently emerges from the present study is one in which two electron pairs participate in the bonding and the other pair belongs mainly to nonbonding regions. [source] Ab-initio simulations of materials using VASP: Density-functional theory and beyondJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2008Jürgen Hafner Abstract During the past decade, computer simulations based on a quantum-mechanical description of the interactions between electrons and between electrons and atomic nuclei have developed an increasingly important impact on solid-state physics and chemistry and on materials science,promoting not only a deeper understanding, but also the possibility to contribute significantly to materials design for future technologies. This development is based on two important columns: (i) The improved description of electronic many-body effects within density-functional theory (DFT) and the upcoming post-DFT methods. (ii) The implementation of the new functionals and many-body techniques within highly efficient, stable, and versatile computer codes, which allow to exploit the potential of modern computer architectures. In this review, I discuss the implementation of various DFT functionals [local-density approximation (LDA), generalized gradient approximation (GGA), meta-GGA, hybrid functional mixing DFT, and exact (Hartree-Fock) exchange] and post-DFT approaches [DFT + U for strong electronic correlations in narrow bands, many-body perturbation theory (GW) for quasiparticle spectra, dynamical correlation effects via the adiabatic-connection fluctuation-dissipation theorem (AC-FDT)] in the Vienna ab initio simulation package VASP. VASP is a plane-wave all-electron code using the projector-augmented wave method to describe the electron-core interaction. The code uses fast iterative techniques for the diagonalization of the DFT Hamiltonian and allows to perform total-energy calculations and structural optimizations for systems with thousands of atoms and ab initio molecular dynamics simulations for ensembles with a few hundred atoms extending over several tens of ps. Applications in many different areas (structure and phase stability, mechanical and dynamical properties, liquids, glasses and quasicrystals, magnetism and magnetic nanostructures, semiconductors and insulators, surfaces, interfaces and thin films, chemical reactions, and catalysis) are reviewed. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Dimerization of CO2 at High Pressure and TemperatureCHEMPHYSCHEM, Issue 9 2005Francesco Tassone Dr. Two,s company: Constant-pressure ab initio molecular dynamics simulations reveal the reaction of two CO2 molecules to form the metastable C2O4 species (see picture) in high-temperature (4000 K) and high-pressure (,20 GPa) liquid CO2. The dimer exhibits a unique Raman-active vibrational mode, which is characteristic for this molecule and consistent with experimental observations. [source] | ||||||||||