The relaxation dynamics of liquids is one of the fundamental problems in liquid physics,and it is also one of the key issues to understand the glass transition mechanism.It will undoubtedly provide enlightenment on understanding and calculating the relaxation dynamics if the molecular orientation flipping images and relevant microparameters of liquids are studied.In this paper,we first give five microparameters to describe the individual molecular string(MS) relaxation based on the dynamical Hamiltonian of the MS model,and then simulate the images of individual MS ensemble,and at the same time calculate the parameters of the equilibrium state.The results show that the main molecular orientation flipping image in liquids(including supercooled liquid) is similar to the random walk.In addition,two pairs of the parameters are equal,and one can be ignored compared with the other.This conclusion will effectively reduce the difficulties in calculating the individual MS relaxation based on the single-molecule orientation flipping rate of the general Glauber type,and the computer simulation time of interaction MS relaxation.Moreover,the conclusion is of reference significance for solving and simulating the multi-state MS model.
It was first proposed that an extended chain Ising (ECI) model contains the Ising chain model,single spin doublewell potentials and a pure phonon heat bath of a specific energy exchange with the spins.The extension method is easy to apply to high dimensional cases.Then the single spin-flip probability (rate) of the ECI model is deduced based on the Boltzmann principle and general statistical principles of independent events and the model is simplified to an extended chain Glauber-Ising (ECGI) model.Moreover,the relaxation dynamics of the ECGI model were simulated by the Monte Carlo method and a comparison with the predictions of the special chain Glauber-Ising (SCGI) model was presented.It was found that the results of the two models are consistent with each other when the Ising chain length is large enough and temperature is relative low,which is the most valuable case of the model applications.These show that the ECI model will provide a firm physical base for the widely used single spin-flip rate proposed by Glauber and a possible route to obtain the single spin-flip rate of other form and even the multi-spin-flip rate.
The string model for the glass transition can quantitatively describe the universal α-relaxation in glassformers.The string relaxation equation (SRE) of the model simplifies the well-known Debye and Rouse-Zimm relaxation equations at high and low enough temperatures,respectively.However,its initial condition,necessary to the further model predictions of glassy dynamics,has not been solved.In this paper,the general initial condition of the SRE for stochastically spatially configurative strings is solved exactly based on the obtained special initial condition of the SRE for straight strings in a previous paper (J.L.Zhang et al.2010 Chin.Phys.B 19,056403).
The string model for the glass transition can quantitatively describe the universal α-relaxation in glassformers,including the average relaxation time,the distribution function of the relaxation time,and the relaxation strength as functions of temperature.The string relaxation equation(SRE) of the model,at high enough temperatures,simplifies to the well-known single particle mean-field Debye relaxation equation,and at low enough temperatures to the well-known Rouse-Zimm relaxation equation that describes the relaxation dynamics of linear macromolecules.However,its initial condition,necessary to the further model predictions of glassy dynamics,has not been solved.In this paper,the special initial condition(SIC) of the SRE,i.e.for straight strings and the dielectric spectrum technique that is one of the most common methods to measure the glassy dynamics,was solved exactly.It should be expected that the obtained SIC would benefit the solution of the general initial condition of the SRE of the string model,i.e.for stochastically spatially configurating strings,as will be described in separate publications.
