Syntax:
-displace_box group-ID parameter args ... keyword value ... +change_box style-
parameter = x or y or z or xy or xz or yz - x, y, z args = style value(s) - style = final or delta or scale or volume - final values = lo hi - lo hi = box boundaries at end of run (distance units) - delta values = dlo dhi - dlo dhi = change in box boundaries at end of run (distance units) - scale values = factor - factor = multiplicative factor for change in box length at end of run - volume value = none = adjust this dim to preserve volume of system - xy, xz, yz args = style value - style = final or delta - final value = tilt - tilt = tilt factor at end of run (distance units) - delta value = dtilt - dtilt = change in tilt factor at end of run (distance units) +ortho = convert simulation box from non-orthogonal (triclinic) to orthogonal + triclinic = convert simulation box from orthogonal to non-orthogonal (triclinic)-
remap value = x or none - x = remap coords of atoms in group into deforming box - none = no remapping of coords - units value = lattice or box - lattice = distances are defined in lattice units - box = distances are defined in simulation box units -- -
Examples:
-displace_box all xy final -2.0 z final 0.0 5.0 units box -displace_box all x scale 1.1 y volume z volume +change_box ortho +change_box triclinicDescription:
-Change the volume and/or shape of the simulation box. Orthogonal -simulation boxes have 3 adjustable parameters (x,y,z). Triclinic -(non-orthogonal) simulation boxes have 6 adjustable parameters -(x,y,z,xy,xz,yz). Any or all of them can be adjusted independently -and simultaneously by this command. This fix can be used to expand or -contract a box, or to apply a shear strain to a non-orthogonal box. +
By default LAMMPS runs a simulation in an orthogonal, axis-aligned +simulation box. LAMMPS can also run simulations in non-orthogonal +(triclinic) simulation boxes. A box is +defined as either orthogonal or non-orthogonal when it is created via +the create_box, read_data, or +read_restart commands.
-Any parameter varied by this command must refer to a periodic -dimension - see the boundary command. For parameters -"xy", "xz", and "yz" this means both affected dimensions must be -periodic, e.g. x and y for "xy". Dimensions not varied by this -command can be periodic or non-periodic. +
This command allows you to toggle the existing simulation box from +orthogonal to non-orthogonal and vice versa. For example, an initial +equilibration simulation can be run in an orthogonal box, the box can +be toggled to non-orthogonal, and then a non-equilibrium MD (NEMD) +simulation can be run with deformation via +the fix deform command.
-The size and shape of the initial simulation box are specified by the -create_box or read_data or -read_restart command used to setup the simulation, -or they are the values from the end of the previous run. The -create_box, read data, and -read_restart commands also determine whether the -simulation box is orthogonal or triclinic and their doc pages explain -the meaning of the xy,xz,yz tilt factors. If the displace_box command -changes the xy,xz,yz tilt factors, then the simulation box must be -triclinic, even if its initial tilt factors are 0.0. -
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- -For the x, y, and z parameters, this is the meaning of their -styles and values. -
-For style final, the final lo and hi box boundaries of a dimension -are specified. The values can be in lattice or box distance units. -See the discsussion of the units keyword below. -
-For style delta, plus or minus changes in the lo/hi box boundaries -of a dimension are specified. The values can be in lattice or box -distance units. See the discussion of the units keyword below. -
-For style scale, a multiplicative factor to apply to the box length -of a dimension is specified. For example, if the initial box length -is 10, and the factor is 1.1, then the final box length will be 11. A -factor less than 1.0 means compression. -
-The volume style changes the specified dimension in such a way that -the box volume remains constant while other box dimensions are changed -explicitly via the styles discussed above. For example, "x scale 1.1 -y scale 1.1 z volume" will shrink the z box length as the x,y box -lengths increase, to keep the volume constant (product of x,y,z -lengths). If "x scale 1.1 z volume" is specified and parameter y is -unspecified, then the z box length will shrink as x increases to keep -the product of x,z lengths constant. If "x scale 1.1 y volume z -volume" is specified, then both the y,z box lengths will shrink as x -increases to keep the volume constant (product of x,y,z lengths). In -this case, the y,z box lengths shrink so as to keep their relative -aspect ratio constant. -
-For solids or liquids, note that when one dimension of the box is -expanded by this command, it may be physically undesirable to hold the -other 2 box lengths constant (unspecified by this command) since that -implies a density change. Using the volume style for those 2 -dimensions to keep the box volume constant may make more physical -sense, but may also not be correct for materials and potentials whose -Poisson ratio is not 0.5. -
-For the scale and volume styles, the box length is expanded or -compressed around its mid point. -
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- -For the xy, xz, and yz parameters, this is the meaning of their -styles and values. Note that changing the tilt factors of a triclinic -box does not change its volume. -
-For style final, the final tilt factor is specified. The value -can be in lattice or box distance units. See the discussion of the -units keyword below. -
-For style delta, a plus or minus change in the tilt factor is -specified. The value can be in lattice or box distance units. See -the discsussion of the units keyword below. -
-All of these styles change the xy, xz, yz tilt factors. In LAMMPS, -tilt factors (xy,xz,yz) for triclinic boxes are always bounded by half -the distance of the parallel box length. For example, if xlo = 2 and -xhi = 12, then the x box length is 10 and the xy tilt factor must be -between -5 and 5. Similarly, both xz and yz must be between --(xhi-xlo)/2 and +(yhi-ylo)/2. Note that this is not a limitation, -since if the maximum tilt factor is 5 (as in this example), then -configurations with tilt = ..., -15, -5, 5, 15, 25, ... are all -equivalent. Any tilt factor specified by this command must be within -these limits. -
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- -The remap keyword determines whether atom positions are re-mapped to -the new box. If remap is set to x (the default), atoms in the fix -group are re-mapped; otherwise they are not. If remap is set to -none, then this remapping does not take place. -
-The units keyword determines the meaning of the distance units used -to define various arguments. A box value selects standard distance -units as defined by the units command, e.g. Angstroms for -units = real or metal. A lattice value means the distance units are -in lattice spacings. The lattice command must have -been previously used to define the lattice spacing. -
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- -The simulation box size or shape can be changed by arbitrarily large -amounts by this command. This is not a problem, except that the -mapping of processors to the simulation box is not changed by this -command from its initial 3d configuration; see the -processors command. Thus, if the box size or shape -changes dramatically, the simulation may not be as well load-balanced -(atoms per processor) as the initial mapping tried to achieve. +
Note that if the simulation box is currently non-orthogonal and has +non-zero tilt in xy, yz, or xz, then it cannot be converted to an +orthogonal box.
Restrictions:
-Any box dimension varied by this fix must be periodic. +
When this command is used, no dumps can be defined, nor +can fix ave/spatial or fix +deform be defined. This is because these commands +test whether the simulation box is orthogonal or not when they are +first issued.
-This command requires inter-processor communication to migrate atoms -once they have moved. This means that your system must be ready to -perform a simulation before using this command (force fields are -setup, atom masses are set, etc). +
Related commands: none
-Related commands: -
- -Default: -
-The option defaults are remap = x and units = lattice. +
Default: none