Syntax:
lattice style value
none value = none for all other styles: value = reduced density (for LJ units) value = cubic lattice constant in Angstroms (for real or metal units)
Examples:
lattice fcc 3.52 lattice hex 0.85 lattice none
Description:
Define a lattice type and lattice constant. This is required before using a commands that (optionally) use the lattice, such as create_atoms or region. The lattice type must be consistent with the dimension of the simulation - see the dimension command. Styles sc or bcc or fcc are for 3d problems. Styles sq or sq2 or hex are for 2d problems. Lattices of style fcc, bcc, sc, or hex are described in any solid-state physics text. A sq lattice is one with atoms at the corners of a square. A sq2 lattice is a sq lattice with an additional atom at the center of the square.
For unit style real or metal, the specified value is the cubic lattice constant in Angstroms. For unit style lj, the value is the reduced density (rho*) which LAMMPS converts into a cubic lattice constant. For 3d problems, the relationship "rho* = rho sigma^3" is used for the conversion, where rho = N/V with V = the volume of the cubic cell and N = 4 for fcc, 2 for bcc, and 1 for sc (simple cubic) lattices. For 2d problems, the relationship "rho* = rho sigma^2" is used for the conversion, where N = 2 for sq2 or hex and 1 for sq. In the hex case, the unit cell is actually rectangular; it is extended by a factor of sqrt(3) in the y-dimension.
The command "lattice none" can be used to turn off the lattice setting. Any command that attempts to use a lattice constant will then generate an error.
Restrictions: none
Related commands:
dimension, orient, origin, create_atoms, region
Default:
lattice none