Simulation Science by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030457181
Publisher: Springer International Publishing

2 Method

We performed a series of classical molecular dynamics simulation of porous SiO material in order to study its vibration characteristics. The target material has one percolated pore, filled with water molecules with varied values of density ranging from to the equilibrium density of water in gas phase, Å. The variation of density is required to observe the transition from dry to water saturated porous material. The vibration spectrum is evaluated by calculating the Fourier transform of the velocity auto-correlation function. The trajectories of the atoms in the simulation system is followed up to 500 ps. The chosen simulation time is suitable to analyze vibration frequencies higher than 1 THz. To obtain data at lower frequency range with a good statistical confidence requires longer simulation time. Therefore, we do not analyze frequencies lower than this value.

We apply Reax Force Field (ReaxFF) potential to model the interaction between atoms. This force field potential allows bond creation and bond breaking of molecules. On that account, it is very suitable to be used to study the chemical processes occurred at the interface between the silicate material and the fluid, as well as the physical response induced by the dynamics of chemical bonds between the surface of the porous material and water molecules. The force field is more computationally convenient in comparison to ab-initio or DFT calculation, with an acceptable accuracy [1, 10, 14]. Using classical molecular dynamics technique, the integration of the force field allows calculation of interactions involving large number of atoms, using considerably low number of CPU cores.

ReaxFF potential consists of terms to handle the complete picture of molecular motion, led by the interaction between atoms. In brief, the total interaction potential is expressed as,

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