Dynamics of Compressed and Stretched Liquid SiO2, and the Glass Transition

1985 ◽  
Vol 63 ◽  
Author(s):  
C. A. Angell ◽  
P. A. Cheeseman ◽  
C. C. Phifer
Keyword(s):  
Glass Transition ◽  
Configuration Space ◽  
Negative Pressure ◽  
Liquid State ◽  
Ion Dynamics ◽  
System Configuration ◽  
Density Maximum ◽  
Pressure Regime ◽  
Dynamics Simulations

ABSTRACTIon dynamics simulations are presented to model the system SiO2 over wide ranges of temperature and density as it passes from liquid into glassy states. Essential features of the diffusive mechanism by means of which the system configuration space is explored are examined in relation to density and structure. The presence of a water-like density maximum in the liquid state of this system is established by using the negative pressure regime to stretch the system and thereby sharpen the phenomenon.

Molecular Dynamics Simulations of Supercooled Liquid Metals and Glasses

2000 ◽  
Vol 644 ◽  
Author(s):  
Hyon-Jee Lee ◽  
Yue Qi ◽  
Alejandro Strachan ◽  
Tahir Cagin ◽  
William A. Goddard ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Liquid State ◽  
Liquid Metals ◽  
Alloy System ◽  
Supercooled Liquid ◽  
Packing Fraction ◽  
Solute Concentration ◽  
Dynamics Simulation ◽  
Dynamics Simulations

AbstractThe thermodynamic, transport and structural properties of a binary metallic glass former in solid, liquid, and glass phases were studied using molecular dynamics simulation. We used a model binary alloy system with a sufficient atomic size mismatch and observed a glass transition in a quenching process. The diffusivity and viscosity were calculated in the liquid state and the super-cooled liquid state. The smaller atom showed higher diffusivity and more configurational randomness compared to the larger atom. The viscosity increased abruptly around the glass transition temperature. The solvent/solute concentration effect on the glass transition was examined in terms of a packing fraction. We find that the glass forming ability increases with the packing fraction in the liquid state because the densely-packed material requires more time to rearrange and crystallize.

Crystal to Glass Transition and Melting in Two Dimensions

1993 ◽  
Vol 321 ◽  
Author(s):  
M. Li ◽  
W. L. Johnson ◽  
W. A. Goddard
Keyword(s):  
Glass Transition ◽  
Intermediate Phase ◽  
Orientational Order ◽  
Finite Size ◽  
Two Dimensions ◽  
Size Difference ◽  
Two Dimensional ◽  
Atomic Size ◽  
Bond Orientational Order ◽  
Dynamics Simulations

ABSTRACTThermodynamic properties, structures, defects and their configurations of a two-dimensional Lennard-Jones (LJ) system are investigated close to crystal to glass transition (CGT) via molecular dynamics simulations. The CGT is achieved by saturating the LJ binary arrays below glass transition temperature with one type of the atoms which has different atomic size from that of the host atoms. It was found that for a given atomic size difference larger than a critical value, the CGT proceeds with increasing solute concentrations in three stages, each of which is characterized by distinct behaviors of translational and bond-orientational order correlation functions. An intermediate phase which has a quasi-long range orientational order but short range translational order has been found to exist prior to the formation of the amorphous phase. The destabilization of crystallinity is observed to be directly related to defects. We examine these results in the context of two dimensional (2D) melting theory. Finite size effects on these results, in particular on the intermediate phase formation, are discussed.

scholarly journals Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6509
Author(s):  
Robert F. Tournier ◽  
Michael I. Ojovan
Keyword(s):  
Glass Transition ◽  
Heating Rate ◽  
Homogeneous Nucleation ◽  
Glassy State ◽  
Singular Values ◽  
Md Simulations ◽  
Melting Temperatures ◽  
Heating And Cooling ◽  
Dynamics Simulations ◽  
Universal Law

A second melting temperature occurs at a temperature Tn+ higher than Tm in glass-forming melts after heating them from their glassy state. The melting entropy is reduced or increased depending on the thermal history and on the presence of antibonds or bonds up to Tn+. Recent MD simulations show full melting at Tn+ = 1.119Tm for Zr, 1.126Tm for Ag, 1.219Tm for Fe and 1.354Tm for Cu. The non-classical homogeneous nucleation model applied to liquid elements is based on the increase of the Lindemann coefficient with the heating rate. The glass transition at Tg and the nucleation temperatures TnG of glacial phases are successfully predicted below and above Tm. The glass transition temperature Tg increases with the heating rate up to Tn+. Melting and crystallization of glacial phases occur with entropy and enthalpy reductions. A universal law relating Tn+ and TnG around Tm shows that TnG cannot be higher than 1.293Tm for Tn+= 1.47Tm. The enthalpies and entropies of glacial phases have singular values, corresponding to the increase of percolation thresholds with Tg and TnG above the Scher and Zallen invariant at various heating and cooling rates. The G-phases are metastable up to Tn+ because the antibonds are broken by homogeneous nucleation of bonds.

scholarly journals Large-Scale Molecular Dynamics Simulations Reveal New Insights Into the Phase Transition Mechanisms in MIL-53(Al)

2021 ◽  
Vol 9 ◽  
Author(s):  
Sander Vandenhaute ◽  
Sven M. J. Rogge ◽  
Veronique Van Speybroeck
Keyword(s):  
Large Scale ◽  
Pressure Control ◽  
Layer By Layer ◽  
Major Step ◽  
Transition Mechanism ◽  
External Pressures ◽  
Pressure Regime ◽  
Dynamics Simulations ◽  
Experimental Crystal ◽  
External Stimuli

Soft porous crystals have the ability to undergo large structural transformations upon exposure to external stimuli while maintaining their long-range structural order, and the size of the crystal plays an important role in this flexible behavior. Computational modeling has the potential to unravel mechanistic details of these phase transitions, provided that the models are representative for experimental crystal sizes and allow for spatially disordered phenomena to occur. Here, we take a major step forward and enable simulations of metal-organic frameworks containing more than a million atoms. This is achieved by exploiting the massive parallelism of state-of-the-art GPUs using the OpenMM software package, for which we developed a new pressure control algorithm that allows for fully anisotropic unit cell fluctuations. As a proof of concept, we study the transition mechanism in MIL-53(Al) under various external pressures. In the lower pressure regime, a layer-by-layer mechanism is observed, while at higher pressures, the transition is initiated at discrete nucleation points and temporarily induces various domains in both the open and closed pore phases. The presented workflow opens the possibility to deduce transition mechanism diagrams for soft porous crystals in terms of the crystal size and the strength of the external stimulus.

Geometry of OH⋯O interactions in the liquid state of linear alcohols from ab initio molecular dynamics simulations

2020 ◽  
Vol 22 (12) ◽  
pp. 6690-6697 ◽  
Author(s):  
Aman Jindal ◽  
Sukumaran Vasudevan
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Bonding ◽  
Ab Initio ◽  
Molecular Dynamics Simulations ◽  
Liquid State ◽  
Crystalline State ◽  
Md Simulations ◽  
Ab Initio Molecular Dynamics ◽  
Linear Alcohols ◽  
Dynamics Simulations

Hydrogen bonding OH···O geometries in the liquid state of linear alcohols, derived from ab initio MD simulations, show no change from methanol to pentanol, in contrast to that observed in their crystalline state.

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