5/7/2021

# # LAMMPS做冲击

## # 如何用LAMMPS模拟冲击压缩？

• 活塞法

fix ID group-ID wall/piston face ... keyword value ...

face = zlo

zero or more keyword/value pairs may be appended

keyword = pos or vel or ramp or units

pos args = z
z = z coordinate at which the piston begins (distance units)

vel args = vz
vz = final velocity of the piston (velocity units)

ramp = use a linear velocity ramp from 0 to vz
ramp args = target damp seed extent
target = target velocity for region immediately ahead of the piston
damp = damping parameter (time units)
seed = random number seed for langevin kicks
extent = extent of thermostatted region (distance units)

units value = lattice or box
lattice = the wall position is defined in lattice units
box = the wall position is defined in simulation box units

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facepos定义了设置的活塞位置，目前face只能是zlo，并沿着z轴正向运动。

velramp定义了活塞的速度。若只使用vel而不使用ramp，活塞将以vel定义的恒定速度运动；若使用ramp，活塞的运动速度将线性变化，且活塞前的区域由langevin恒温器控温，区域随活塞一起运动，区域大小由extent定义。

• 反射壁法

fix ID group-ID wall/reflect face arg ... keyword value ...

face = xlo or xhi or ylo or yhi or zlo or zhi

arg = EDGE or constant or variable
EDGE = current lo edge of simulation box
constant = number like 0.0 or 30.0 (distance units)
variable = equal-style variable like v_x or v_wiggle

keyword = units

units value = lattice or box
lattice = the wall position is defined in lattice units
box = the wall position is defined in simulation box units

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face arg指出了设置的反射壁的位置，可以是EDGE、常数或变量。

keyword value指出了arg-constant中距离单位的含义。

• MSST法