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3¡¢ÎÄÏ×ÖÐ˵The simulation process is divided into three parts: the velocity-scaling period, the equilibration period, and the heating period. During the velocity-scaling period 0¨C500 ps, the velocity of each argon atom is scaled at every time step so that the system temperature remains constant. This is followed by the equilibration period 500¨C1000 ps in which the velocity scaling is removed, and the argon atoms are allowed to move freely and equilibrate. The wall temperature during these two steps is the same as the initial system temperature. At the start of the heating period 1000¨C4000 ps, the wall temperatures are step changed to a different temperature, and the heating and/or cooling process of the argon is observed.
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The simulation domain is a nanochannel in the form of a cuboid£¬ The domain consists of two platinum Pt walls and argon Ar fluid. Pt atoms, arranged in a fcc 111 structure, constitute the Pt wall. The x and y dimensions are 6.117 nm6.117 nm, respectively; the z direction represents the channel height. A thin liquid argon film of thickness t film is placed on each Pt wall. The remaining volume is occupied by argon vapor. Both liquid and vapor are initially at their respective saturation states at 90 K. The simulation domain contains 3465 Pt atoms. The time step is 5 fs. The atomic interaction is governed by the modified Lennard-Jones LJ potential, as defined by Stoddard and Ford,14 U MLJr = 4 r12 − r6 +6r cut12 − 3r cut6 rcut r 2 −7r cut12 − 4r cut6 . 1
The above potential form is employed for both Ar¨CAr and Ar¨CPt interactions with the following values: Ar¨CAr=3.4 10−10 m, Ar¨CAr=1.6710−21 J, Ar¨CPt=3.08510−10 m, and Ar¨CPt=0.89410−21 J. The cutoff radius for both Ar¨CAr and Ar¨CPt interactions is set as r cut=4Ar¨CAr. The force of interaction is calculated from the potential function as follows: F =−U. The argon atoms are subjected to six boundaries, two in each of the x, y, and z directions. The boundaries in the x and y directions are periodic. The boundaries in the z direction are the Pt walls. The ¡°fluid-wall thermal equilibrium model¡± is used to numerically simulate heat transfer
between wall and fluid atoms.1,15 The equations and parameters implemented are nondimensional.16 The algorithm used to calculate the atomic force interactions is the linked-cell algorithm, which is a cell-based method and involves data organization.17 The integrator method used here is the velocity-Verlet method.18 The simulation process is divided into three parts: the velocity-scaling period, the equilibration period, and the heating period. During the velocity-scaling period 0¨C500 ps, the velocity of each argon atom is scaled at every time step so that the system temperature remains constant. This is followed by the equilibration period 500¨C1000 ps in which the velocity scaling is removed, and the argon atoms are allowed to move freely and equilibrate. The wall temperature during these two steps is the same as the initial system temperature. At the start of the heating period 1000¨C4000 ps, the wall temperatures are step changed to a different temperature, and the heating and/or cooling process of the argon is observed.
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