First-principles study on the specific heat of glass at glass transition with a case study on glycerol

Abstract

The standard method to determine the transition temperature (Tg) of glass transition is the jump in the specific heat. Despite this importance, standard theory for this jump is lacking. The difficulties encompass from lack of proper treatments of specific heat of liquids, hysteresis, to the timescale issue. The first part of this paper provides a non-empirical method to calculate specific heat of glass. The method consists of molecular dynamics (MD) simulations based on density-functional theory (DFT) and thermodynamics methods. The total-energy approach based on DFT enables us to calculate specific heat, irrespective of solids or liquids. A serious problem for glass-transition states is involvement of complicated energy dissipation processes, which is resolved by adiabatic MD simulations. The problems of hysteresis and the timescale issue are alleviated by restricting the scope of calculations to equilibrium states only. The second part of this paper describes an application of the theory to the specific-heat jump (Delta Cp) of glycerol in order to show the validity of the methods. Despite severe limitations due to the small size of supercells, a reasonable value for the specific-heat jump is obtained. By decomposing Delta Cp into contributions of the structural energy, phonon, and thermal expansion parts, we have a sound interpretation for the Delta Cp: the major contribution to Delta Cp comes from the change in the structural energy. From this, a neat energy diagram about the glass transition is obtained. An outcome of this study is verification of the empirical relationship between the fragility and specific-heat jump. These two energies are scaled by the ratio k=Tg/ Delta T, where Delta T is the width of the transition, through which the two quantities are interrelated. This is useful for organizing various relationships that are found empirically.

References in corpus (18)

• Theoretical perspective on the glass transition and amorphous materials
• Theory of Structural Glasses and Supercooled Liquids
• Dynamics on the Way to Forming Glass: Bubbles in Space-time
• Fragilities of Liquids Predicted from the Random First Order Transition Theory of Glasses
• Coarse-grained microscopic model of glass formers
• The phonon theory of liquid thermodynamics
• Barrier Softening near the onset of Non-Activated Transport in Supercooled Liquids: Implications for Establishing Detailed Connection between Thermodynamic and Kinetic Anomalies in Supercooled Liquids
• Perspective: Configurational entropy of glass-forming liquids
• Ehrenfest relations at the glass transition: solution to an old paradox
• Landscape equivalent of the shoving model
• Thermodynamic and structural aspects of the potential energy surface of simulated water
• Calorimetric glass transition explained by hierarchical dynamic facilitation
• Heat capacity at the glass transition
• Atomistic structural mechanism for the glass transition: Entropic contribution
• Are defect models consistent with the entropy and specific heat of glass-formers?
• Interpretation of the apparent activation energy of glass transition
• Theory of Specific Heat in Glass Forming Systems
• Dynamical and orientational structural crossovers in low-temperature glycerol