Search results for "molecular dynamics"
showing 10 items of 1075 documents
Molecular dynamics simulations of colloids: Supercooled Yukawa systems
2007
We performed molecular dynamics simulations on one and two component Yukawa systems. Cooling the system down and inspecting pair distribution functions (pdf) and bond correlation functions (bcf) we found the one component system to crystallize into a bcc-like lattice rather than an fcc lattice which is the stable phase of the simulated system at low temperatures. Upon cooling the two component system freezes into a glassy state without exhibiting crystalline structure in pdf or bcf. We define particle excess functions which show that spacial fluctuations in the number density of particles of the different components decay quite slowly. Therefore we believe that a well defined state of the t…
Experimental and theoretical study of stereoelectronic and H-bond control of reactivity in α- and β-methyl d-glucopyranoside ozonolysis
1998
Abstract The topography of the molecular electrostatic potential (MEP) of α and β anomers of methyl d -glucopyranosides has been used to analyze the reactivity of these species towards electrophilic attack and to complete the results we obtained during the ozonation reaction. Molecular mechanics (MM) and molecular dynamics (MD) simulations have been performed to screen the conformational space of α- and β-methyl d -glucopyranosides in order to determine the chair conformations which correspond to a global minimum energy conformation. Density Functional Theory (DFT) (Faststructure) and PM3 (semiempirical) calculations have been carried out to refine the geometries of the 4 C 1 and 1 C 4 chai…
Energy-Stable Numerical Schemes for Multiscale Simulations of Polymer–Solvent Mixtures
2017
We present a new second-order energy dissipative numerical scheme to treat macroscopic equations aiming at the modeling of the dynamics of complex polymer–solvent mixtures. These partial differential equations are the Cahn-Hilliard equation for diffuse interface phase fields and the Oldroyd-B equations for the hydrodynamics of the polymeric mixture. A second-order combined finite volume/finite difference method is applied for the spatial discretization. A complementary approach to study the same physical system is realized by simulations of a microscopic model based on a hybrid Lattice Boltzmann/Molecular Dynamics scheme. These latter simulations provide initial conditions for the numerical…
Comparison of model potentials for molecular-dynamics simulations of silica.
2005
Structural, thermomechanical, and dynamic properties of pure silica SiO2 are calculated with three different model potentials, namely, the potential suggested by van Beest, Kramer, and van Santen (BKS) [Phys. Rev. Lett. 64, 1955 (1990)], the fluctuating-charge potential with a Morse stretch term for the short-range interactions proposed by Demiralp, Cagin, and Goddard (DCG)[Phys. Rev. Lett. 82, 1708 (1999)], and a polarizable force field proposed by Tangney and Scandolo (TS) [J. Chem. Phys. 117, 8898 (2002)]. The DCG potential had to be modified due to flaws in the original treatment. While BKS reproduces many thermomechanical properties of different polymorphs rather accurately, it also sh…
Influence of chain length on the molecular dynamics of an aliphatic ionene
1998
An aliphatic random copolymer ionene (a cationic polyelectrolyte with N + in the repeat unit), was fractionated with the continuous polymer fractionation and investigated for its molecular weight dependent properties. The fractions were analyzed with GPC and capillary viscometry for their molecular weight. Glass transition temperatures were determined with DSC and a strong molecular weight dependence was observed, but no influence in the ionic conductivity was observed. The temperature dependency of ionic conductivity in ionenes is described.
The Fluorite/Water Interfaces: Structure and Spectroscopy from First Principles Simulations
2014
Despite its relevance to industrial, environmental and medical application, the fluorite/water interface still lacks a microscopic/atomistic characterization. In this contribution we provide the first atomistic description of such interface using first principles molecular dynamics simulations. Our models, which explore a wide range of pH, are able to provide a rational of the recent vibrational spectroscopy experiments. In particular we find that at neutral pH the water at the interface is disordered, in agreement with the experimental data, and explaining why no Vibrational Sum Frequency Generation (VSFG) signal is recorded. At high pH, OH groups which localize at the interface are respon…
Pillar[n]arenes-a Novel, Highly Promising Class of Macrocyclic Host Molecules
2014
Since 2008 a new field of supramolecular chemistry has developed rapidly: the chemistry of pillar[n]arenes. These “younger brothers and sisters” of calixarenes are conveniently accessible and extremely guest-friendly. Guests from many different classes of organic compounds are welcome. Nevertheless, a high selectivity for the threading of guest molecules in the macrocyclic cavities can be achieved. The complex stability is characterized by association constants Ka between 10 and 1×108 M−1. The rate constants of the threading vary over several orders of magnitude. The focus of this article lies on the preparation (sections 2 and 3) and the structures (section 4) of pillar[n]arenes (n=5–10) i…
The Effects of the Electron-Phonon Interaction on the Vibrational Anomalies and Polymorphism in Titanium
1997
AbstractWe apply the frozen phonon and molecular dynamics methods within the semiempirical orthogonal tight-binding framework to study the anomalous behaviour of the (0001) optical longitudinal (LO) and transverse (TO) phonons in the low temperature hep phase of Ti, and the ⅔[111]L and ½[110]T1 phonons in the high temperature bec phase. We demonstrate that, in agreement with previous findings in Zr, the anomalous thermal frequency shifts in hep Ti are related to the strong coupling of the electron density of states (DOS) to the particular lattice distortions. The distortions along the bec ⅔[111]L and ½[110]T1 phonons also significantly affect the DOS, resulting in the instability of these m…
Local structure and lattice dynamics of cubic Y2O3: an x-ray absorption spectroscopy study
2015
Classical molecular dynamics was used to interpret the temperature dependent (300-1273 K) Y K-edge x-ray absorption spectra of cubic c-Y2O3 and to validate two force-field models. It was shown that both models reproduce well thermal disorder effect, however are less accurate in description of static octahedra distortion around yttrium atoms. The temperature dependencies of mean-square displacements and mean-square relative displacements were obtained from molecular dynamics simulations for the first two shells of yttrium. The importance of anharmonic effects was demonstrated by comparison of molecular dynamics and lattice dynamics results.
The Mixed Akali Effect in Ternary Alkali Silicate Melts: Insight from Molecular Dynamics Computer simulations
2005
Large scale molecular dynamics (MD) computer simulations are used to study the amorphous alkali silicates (Li2O)(2·SiO2) [LS2], (K2O)(2·SiO2) [KS2], and (0.5·Li2O)(0.5·K2O)(2·SiO2) [LKS2]. These systems are characterized by a fast alkali ion motion in a relatively immobile Si-0 matrix. We investigate the so-called mixed alkali effect (MAE) which is reflected as a significant decrease of the alkali ion diffusion constants in LKS2 as compared to the corresponding binary systems LS2 and KS2. We show that the subtle interplay between the structure on intermediate length scales and the alkali diffusion is important to understand the microscopic origin of the MAE.