create_particles command

Syntax

create_particles template-ID style args keyword values ...
  • template-ID = ID of a fix of type particletemplate/*
  • style = single
single args = x y z
  x,y,z = coordinates of a single atom (distance units)
  • zero or more keyword/value pairs may be appended
  • keyword = units or velocity or omega or orientation or rotate
units value = lattice or box
  lattice = the geometry is defined in lattice units
  box = the geometry is defined in simulation box units
velocity values = vx vy vz
  vx, vy, vz = x-, y- and z-component of velocity (velocity units)
omega values = omegax omegay omegaz
  omegax, omegay, omegaz = x-, y- and z-component of angular velocity (1/ time units)
orientation values = q1 q2 q3 q4
  q1, q2, q3, q4 = quaternion values for desired orientation
rotate values = axis ax ay az angle ang
  axis = obligatory keyword
  ax, ay, az = axis vector for rotation (length units)
  angle = obligatory keyword
  ang = rotation angle (degrees)

Examples

create_particles pts single 0 0 5 velocity 0 0 -1

Description

This command creates a single particle as an alternative to reading in their coordinates explicitly via a read_data or read_restart command. A simulation box must already exist, which is typically created via the create_box command. In case of units = lattice, a lattice must also be defined using the lattice command.

The kind of particles is defined by the fix particletemplate/* given by template-ID (e.g. sphere ). Unless otherwise specified per-atom properties are initialized with their default settings.

For the single style, a single atom is added to the system at the specified coordinates. This can be useful for debugging purposes or to create a tiny system with a handful of particles at specified positions.

The units keyword determines the meaning of the distance units used to specify the coordinates of the one atom created by the single style. 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 velocity keyword allows to set the initial velocity of the particle. Similarly, the omega keyword sets the initial angular velocity of the inserted particles.

The orientation keyword is one way to set the particles orientation in space. Obviously, this keyword makes only sense for particle templates that track the particles orientation like superquadric . For everybody not familiar with quaternions the keyword rotate is an alternative. It allows to define particle orientation by providing axis and angle. Further it is possible to do several rotations consecutively.

Note that this command adds atoms to those that already exist. By using the create_particles command multiple times, multiple sets of atoms can be added to the simulation. For example, interleaving create_particles with lattice commands specifying different orientations, grain boundaries can be created. By using the create_particles command in conjunction with the delete_atoms command, reasonably complex geometries can be created. The create_particles command can also be used to add atoms to a system previously read in from a data or restart file. In all these cases, care should be taken to insure that new atoms do not overlap existing atoms inappropriately. The delete_atoms command can be used to handle overlaps.

Atom IDs are assigned to created atoms in the following way. The collection of created atoms are assigned consecutive IDs that start immediately following the largest atom ID existing before the create_particles command was invoked. When a simulation is performed on different numbers of processors, there is no guarantee a particular created atom will be assigned the same ID.

The set command can be used to override many of the default settings.

Restrictions

An atom_style must be previously defined to use this command.

Default

units = box, velocity = 0. 0. 0., omega = 0. 0. 0., orientation = 1. 0. 0. 0.