| Molecular dynamics(MD)simulation has become an important tool for studying micro-or nano-scale dynamics and the statistical properties of fluids and solids.In MD simulations,there are mainly two approaches:equilibrium and non-equilibrium molecular dynamics(EMD and NEMD).In this paper,a new energy conversion based correction(ECBC)method for MD is developed.Unlike the traditional systematic correction based on macroscopic parameters,the ECBC method is developed strictly based on the physical interaction processes between the pair of molecules or atoms.The developed ECBC method can apply to EMD and NEMD directly.While using MD with this method,the difference between the EMD and NEMD is eliminated,and no macroscopic parameters such as external imposed potentials or coefficients are needed.With this method,many limits of using MD are lifted.The application scope of MD is greatly extended.The Brownian motion of the nano-particle in fluid depends on the molecular forces acting on it.Because of the small size and the high frequency,it is difficult to make experimental measurement of the force.In present work,Brownian forces acting on the nano-particle are numerical investigated with the molecular dynamics method.Some new phenomena are disclosed.(1)The probability distribution shows the Brownian forces conform to the Gaussian distribution,and the self-similarity of the probability distribution is also found for different 1/Kn numbers.(2)The frequency spectrum distribution of the Brownian force is not a white noise,which is different from the assumption commonly used in Langevin model.The preferential frequency of the Brownian force is found.(3)The size effect that the Brownian forces is not monotonically varying with the size of the nanoparticles is also found.It increases first and then decreases after it reaches the maximum value at 1/Kn ?250.The variation process for 1/Kn<250 observed in present work has not been reported in previous research yet. |
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