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### atom_modify command

Syntax:

    atom_modify keyword value ...

- one or more keyword/value pairs may be appended
- keyword = map

        map value = array or hash

Examples:

    atom_modify map hash

Description:

Modify properties of the atom style selected within LAMMPS.

The map keyword determines how atom ID lookup is done for molecular problems. Lookups are performed by bond (angle, etc) routines in LAMMPS to find the local atom index associated with a global atom ID. When the array value is used, each processor stores a lookup table of length N, where N is the total # of atoms in the system. This is the fastest method for most simulations, but a processor can run out of memory to store the table for very large simulations. The hash value uses a hash table to perform the lookups. This method can be slightly slower than the array method, but its memory cost is proportional to N/P on each processor, where P is the total number of processors running the simulation.

Restrictions:

This command must be used before the simulation box is defined by a read_data or create_box command.

Related commands: none

Default:

By default, atomic (non-molecular) problems do not allocate maps. For molecular problems, the option default is map = array.