1. What are the contributions mentioned in the paper "Rigid molecule approximation in memory function-based models for molecular liquids: application to liquid water" ?
In the present article the authors show how models for simple liquids can be used to describe the dynamics of atoms in molecular liquids within the rigid molecule approximation.. The authors show in particular that the atomic masses are to be replaced by the corresponding Sachs-Teller masses and they derive a formal expression for the so-called Einstein frequency.
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2. What are the future works mentioned in the paper "Rigid molecule approximation in memory function-based models for molecular liquids: application to liquid water" ?
Using indepth analyses of MD trajectories of liquid water the authors were able to show that the validity of an existing model for the center-of-mass dynamics can be considerably extended to describe not only the diffusive motions seen in quasielastic neutron scattering experiments, but also faster motions, such as intermolecular vibrations and molecular librations.. The authors have shown how this model can be extended to describe also the atomic dynamics in liquids consisting of rigid or semi-rigid molecules.. This extension concerns the mean square velocity, for which an analytical expression can be derived from the molecular geometry, and the so-called Einstein frequency, which is the initial value of the memory function associated with the velocity autocorrelation function.
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![Fig. 6. First order and second order memory functions of the incoherent intermediate scattering function for water at ambient temperature and pressure for q = 10 nm–1 and q = 32 nm–1, as obtained from AR analysis of MD trajectories (solid lines) and from the analytical model using the parameters given in Table 1 (dotted lines). The insets show zooms on the corresponding functions. Part of the data have been taken from Ref. [12].](/figures/fig-6-first-order-and-second-order-memory-functions-of-the-2jrxo45j.webp)
![Table 1. Fitted values for the parameters of the analytical model. The parameters have been obtained from fits to the simulated dynamic structure factor shown in Fig. 1. The data have been taken from Ref. [12].](/figures/table-1-fitted-values-for-the-parameters-of-the-analytical-3rzaktq7.webp)
![Fig. 7. Fourier transform of the average velocity autocorrelation function of the hydrogen atom in water at ambient temperature and pressure obtained from MD simulation (solid line) and from the analytical model using the parameters given in Table 1 (dotted line). The data have been taken from Ref. [12].](/figures/fig-7-fourier-transform-of-the-average-velocity-35cugzvh.webp)
