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"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Commands_all.html)
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:line
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fix wall/stochastic command :h3
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[Syntax:]
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fix ID group-ID wall/stochastic reflectionstyle face pos temp velx vely velz accomx accomy accomz ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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wall/stochastic = style name of this fix command :l
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one or more face/arg pairs may be appended :l
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reflectionstyle = diffusive or maxwell or cercignanilampis :l
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face = {xlo} or {xhi} or {ylo} or {yhi} or {zlo} or {zhi} :l
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{xlo},{ylo},{zlo} pos = EDGE or constant
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EDGE = current lo edge of simulation box
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constant = number like 0.0 or -30.0 (distance units)
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temp = wall temperature
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velx, vely, velz = wall velocity along x, y, z directions
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accomx, accomy, accomz = accommodation coefficients along x, y, z directions (only for maxwell and cercignanilampis reflection style)
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{xhi},{yhi},{zhi} pos = EDGE or constant or variable
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EDGE = current hi edge of simulation box
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constant = number like 50.0 or 100.3 (distance units)
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temp = wall temperature
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velx, vely, velz = wall velocity along x, y, z directions
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accomx, accomy, accomz = accommodation coefficients along x, y, z directions (only for maxwell and cercignanilampis style) :pre
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zero or more keyword/value pairs may be appended :l
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keyword = {units} :l
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{units} value = {lattice} or {box}
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{lattice} = the wall position is defined in lattice units
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{box} = the wall position is defined in simulation box units :pre
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:ule
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[Examples:]
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fix zwalls all wall/stochastic diffusive zlo EDGE 300 0.1 0.1 0 zhi EDGE 200 0.1 0.1 0
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fix ywalls all wall/stochastic maxwell ylo 5.0 300 0.1 0.0 0.0 0.8 yhi 10.0 300 0.1 0.0 0.0 0.8
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fix xwalls all wall/stochastic cercignanilampis xlo 0.0 300 0.0 0.1 0.9 0.8 0.7 xhi EDGE 300 0.0 0.1 0 0.9 0.8 0.7 units box :pre
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[Description:]
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This fix differs from the command fix wall/reflect which is equivalent
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to the mirror reflection in that the post collision velocity of the atoms
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in the stochastic wall is random. The randomness can come from many sources:
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thermal motion of solid atoms, the surface roughness, etc... Three
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stochastic wall models are implemented.
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Diffusive wall (reflectionstyle = diffusive): all the gas atoms are
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reflected diffusively. Their velocity distribution corresponds to the
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equilibrium distribution at the wall temperature.
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Maxwell model (reflectionstyle = maxwell): the reflection is partially
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diffusive and partially specular. The accommodation coefficient is the
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portion of the diffusive reflection "Maxwell"_#Maxwell.
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Cercignani/Lampis model: 3 accommodations coefficients are used, two
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velocity accommodation coefficients and one normal kinetic energy
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accommodation "CL"_#CL, "To"_#To. The code will recognize automatically
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the normal direction of the wall and the other two tangential
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directions. For example, if accomx = 0.5, accomy = 0.2, accomz = 0.3 and
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the wall is normal to direction y, accomx and accomz are the tangential
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velocity accommodation coefficients and accomy is the normal kinetic
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energy accommodation coefficients.
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The {units} keyword determines the distance units used to define a wall
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position. A {box} value selects standard distance units as defined by
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the "units"_units.html command, e.g. Angstroms for units = real or
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metal. A {lattice} value means the distance units are in lattice
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spacings. The "lattice"_lattice.html command must have been previously
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used to define the lattice spacings.
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:line
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[Restrictions:]
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Due to the similarities, this fix has the same limitation as the the
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wall/reflect. Any dimension (xyz) that has a wall must be non-periodic. It
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should not be used with rigid bodies such as those defined by a "fix rigid"
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command. Furthermore, the wall velocity must lie on the same plane as the wall. Package USER-MISC is required to use this fix.
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[Related commands:]
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"fix wall/reflect"_fix_wall_reflect.html,
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[Default:] none
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:line
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:link(Maxwell)
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[(Maxwell)] J.C. Maxwell, Philos. Tans. Royal Soc. London, 157: 49-88 (1867).
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:link(CL)
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[(Cercignani)] C. Cercignani and M. Lampis. Trans. Theory Stat. Phys. 1, 2, 101 (1971).
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:link(To)
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[(To)] Q.D. To, V.H. Vu, G. Lauriat, and C. Leonard. J. Math. Phys. 56, 103101 (2015).
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"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Commands_all.html)
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:line
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fix wall/stochastic command :h3
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[Syntax:]
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fix ID group-ID wall/stochastic reflectionstyle seed face pos temp velx vely velz accomx accomy accomz ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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wall/stochastic = style name of this fix command :l
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one or more face/arg pairs may be appended :l
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reflectionstyle = diffusive or maxwell or cercignanilampis :l
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seed = random seed for stochastic wall (must be less than 900000000) :l
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face = {xlo} or {xhi} or {ylo} or {yhi} or {zlo} or {zhi} :l
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{xlo},{ylo},{zlo} pos = EDGE or constant
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EDGE = current lo edge of simulation box
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constant = number like 0.0 or -30.0 (distance units)
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temp = wall temperature
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velx, vely, velz = wall velocity along x, y, z directions
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accomx, accomy, accomz = accommodation coefficients along x, y, z directions (only for maxwell and cercignanilampis reflection style)
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{xhi},{yhi},{zhi} pos = EDGE or constant or variable
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EDGE = current hi edge of simulation box
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constant = number like 50.0 or 100.3 (distance units)
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temp = wall temperature
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velx, vely, velz = wall velocity along x, y, z directions
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accomx, accomy, accomz = accommodation coefficients along x, y, z directions (only for maxwell and cercignanilampis style) :pre
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zero or more keyword/value pairs may be appended :l
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keyword = {units} :l
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{units} value = {lattice} or {box}
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{lattice} = the wall position is defined in lattice units
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{box} = the wall position is defined in simulation box units :pre
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:ule
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[Examples:]
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fix zwalls all wall/stochastic diffusive 23424 zlo EDGE 300 0.1 0.1 0 zhi EDGE 200 0.1 0.1 0
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fix ywalls all wall/stochastic maxwell 345533 ylo 5.0 300 0.1 0.0 0.0 0.8 yhi 10.0 300 0.1 0.0 0.0 0.8
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fix xwalls all wall/stochastic cercignanilampis 2308 xlo 0.0 300 0.0 0.1 0.9 0.8 0.7 xhi EDGE 300 0.0 0.1 0 0.9 0.8 0.7 units box :pre
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[Description:]
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This fix differs from the command fix wall/reflect which is equivalent
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to the mirror reflection in that the post collision velocity of the atoms
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in the stochastic wall is random. The randomness can come from many sources:
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thermal motion of solid atoms, the surface roughness, etc... Three
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stochastic wall models are implemented.
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Diffusive wall (reflectionstyle = diffusive): all the gas atoms are
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reflected diffusively. Their velocity distribution corresponds to the
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equilibrium distribution at the wall temperature.
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Maxwell model (reflectionstyle = maxwell): the reflection is partially
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diffusive and partially specular. The accommodation coefficient is the
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portion of the diffusive reflection "Maxwell"_#Maxwell.
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Cercignani/Lampis model: 3 accommodations coefficients are used, two
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velocity accommodation coefficients and one normal kinetic energy
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accommodation "CL"_#CL, "To"_#To. The code will recognize automatically
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the normal direction of the wall and the other two tangential
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directions. For example, if accomx = 0.5, accomy = 0.2, accomz = 0.3 and
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the wall is normal to direction y, accomx and accomz are the tangential
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velocity accommodation coefficients and accomy is the normal kinetic
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energy accommodation coefficients.
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The {units} keyword determines the distance units used to define a wall
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position. A {box} value selects standard distance units as defined by
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the "units"_units.html command, e.g. Angstroms for units = real or
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metal. A {lattice} value means the distance units are in lattice
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spacings. The "lattice"_lattice.html command must have been previously
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used to define the lattice spacings.
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:line
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[Restrictions:]
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Due to the similarities, this fix has the same limitation as the the
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wall/reflect. Any dimension (xyz) that has a wall must be non-periodic. It
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should not be used with rigid bodies such as those defined by a "fix rigid"
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command. Furthermore, the wall velocity must lie on the same plane as the wall. Package USER-MISC is required to use this fix.
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[Related commands:]
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"fix wall/reflect"_fix_wall_reflect.html,
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[Default:] none
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:line
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:link(Maxwell)
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[(Maxwell)] J.C. Maxwell, Philos. Tans. Royal Soc. London, 157: 49-88 (1867).
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:link(CL)
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[(Cercignani)] C. Cercignani and M. Lampis. Trans. Theory Stat. Phys. 1, 2, 101 (1971).
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:link(To)
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[(To)] Q.D. To, V.H. Vu, G. Lauriat, and C. Leonard. J. Math. Phys. 56, 103101 (2015).
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