\(\renewcommand{\AA}{\text{Å}}\)

fix store/state command

Syntax

fix ID group-ID store/state N input1 input2 ... keyword value ...

ID, group-ID are documented in fix command
store/state = style name of this fix command
N = store atom attributes every N steps, N = 0 for initial store only

input = one or more atom attributes

possible attributes = id, mol, type, mass,
                      x, y, z, xs, ys, zs, xu, yu, zu, xsu, ysu, zsu, ix, iy, iz,
                      vx, vy, vz, fx, fy, fz,
                      q, mux, muy, muz, mu,
                      radius, diameter, omegax, omegay, omegaz,
                      angmomx, angmomy, angmomz, tqx, tqy, tqz,
                      c_ID, c_ID[I], f_ID, f_ID[I], v_name,
                      d_name, i_name, i2_name[I], d2_name[I],

id = atom ID
mol = molecule ID
type = atom type
mass = atom mass
x,y,z = unscaled atom coordinates
xs,ys,zs = scaled atom coordinates
xu,yu,zu = unwrapped atom coordinates
xsu,ysu,zsu = scaled unwrapped atom coordinates
ix,iy,iz = box image that the atom is in
vx,vy,vz = atom velocities
fx,fy,fz = forces on atoms
q = atom charge
mux,muy,muz = orientation of dipolar atom
mu = magnitued of dipole moment of atom
radius,diameter = radius.diameter of spherical particle
omegax,omegay,omegaz = angular velocity of spherical particle
angmomx,angmomy,angmomz = angular momentum of aspherical particle
tqx,tqy,tqz = torque on finite-size particles
c_ID = per-atom vector calculated by a compute with ID
c_ID[I] = Ith column of per-atom array calculated by a compute with ID
f_ID = per-atom vector calculated by a fix with ID
f_ID[I] = Ith column of per-atom array calculated by a fix with ID
v_name = per-atom vector calculated by an atom-style variable with name
i_name = custom integer vector with name
d_name = custom floating point vector with name
i2_name[I] = Ith column of custom integer array with name
d2_name[I] = Ith column of custom floating-point array with name

zero or more keyword/value pairs may be appended
keyword = com
```
com value = yes or no
```

Examples

fix 1 all store/state 0 x y z
fix 1 all store/state 0 xu yu zu com yes
fix 2 all store/state 1000 vx vy vz

Description

Define a fix that stores attributes for each atom in the group at the time the fix is defined. If N is 0, then the values are never updated, so this is a way of archiving an atom attribute at a given time for future use in a calculation or output. See the discussion of output commands that take fixes as inputs.

If N is not zero, then the attributes will be updated every N steps.

Note

Actually, only atom attributes specified by keywords like xu or vy or radius are initially stored immediately at the point in your input script when the fix is defined. Attributes specified by a compute, fix, or variable are not initially stored until the first run following the fix definition begins. This is because calculating those attributes may require quantities that are not defined in between runs.

The list of possible attributes is the same as that used by the dump custom command, which describes their meaning.

If the com keyword is set to yes then the xu, yu, and zu inputs store the position of each atom relative to the center-of-mass of the group of atoms, instead of storing the absolute position.

The requested values are stored in a per-atom vector or array as discussed below. Zeroes are stored for atoms not in the specified group.

Restart, fix_modify, output, run start/stop, minimize info

This fix writes the per-atom values it stores to binary restart files, so that the values can be restored when a simulation is restarted. See the read_restart command for info on how to re-specify a fix in an input script that reads a restart file, so that the operation of the fix continues in an uninterrupted fashion.

Warning

When reading data from a restart file, this fix command has to be specified exactly the same way as before. LAMMPS will only check whether a fix is of the same style and has the same fix ID and in case of a match will then try to initialize the fix with the data stored in the binary restart file. If the fix store/state command does not match exactly, data can be corrupted or LAMMPS may crash.

None of the fix_modify options are relevant to this fix.

If a single input is specified, this fix produces a per-atom vector. If multiple inputs are specified, a per-atom array is produced where the number of columns for each atom is the number of inputs. These can be accessed by various output commands. The per-atom values be accessed on any timestep.

No parameter of this fix can be used with the start/stop keywords of the run command. This fix is not invoked during energy minimization.

Restrictions

none

Default

The option default is com = no.