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pair_style hybrid command

Syntax:

pair_style hybrid style1 style2 ... 

Examples:

pair_style hybrid lj/charmm/coul/long 10.0 eam
pair_coeff 1*2 1*2 eam niu3
pair_coeff 3 3 lj/cut/coul/cut 1.0 1.0
pair_coeff 1*2 3 lj/cut 0.5 1.2 

Description:

The hybrid style enables the use of multiple pair styles in one simulation. A pair style can be assigned to each pair of atom types via the pair_coeff command.

For example, a metal on a LJ surface could be computed where the metal atoms interact with each other via a eam potential, the surface atoms interact with each other via a lj/cut potential, and the metal/surface interaction is also via a lj/cut potential.

All pair styles that will be used must be listed in the pair_style hybrid command (in any order). The name of each sub-style is followed by its arguments, as illustrated in the example above.

In the pair_coeff command, the first coefficient sets the pair style and the remaining coefficients are those appropriate to that style. For example, consider a simulation with 3 atom types: types 1 and 2 are Ni atoms, type 3 are LJ atoms with charges. The following commands would set up a hybrid simulation:

pair_style hybrid eam/alloy lj/cut/coul/cut 10.0 lj/cut 8.0
pair_coeff * * eam/alloy nialhjea 1 1 0
pair_coeff 3 3 lj/cut/coul/cut 1.0 1.0
pair_coeff 1*2 3 lj/cut 0.8 1.1 

If the pair_coeff command for a sub-style requires the use of * * as atom type arguments (e.g. the eam/alloy example above), then it will also include trailing arguments which map atom types to elements in the potential. These mapping arguments should be specified as 0 if the sub-style is not being applied to certain atom types.

Note that you may also need to use an atom_style hybrid command in your input script, if atoms in the simulation will have attributes from several atom styles, due to using multiple pair potentials.


Mixing, shift, table, tail correction, per-atom energy/stress, and restart info:

Any pair potential settings made via the pair_modify command are passed along to all sub-styles of the hybrid potential.

For atom type pairs I,J and I != J, if the sub-style assigned to I,I and J,J is the same, and if the sub-style allows for mixing, then the coefficients for I,J can be mixed. The default mix value is geometric. See the "pair_modify" command for details. See the See the doc page for the sub-style to see if allows for mixing.

The hybrid pair style supports the pair_modify shift, table, and tail options for an I,J pair interaction, if the associated sub-style supports it.

The hybrid pair style can calculate per-atom energy and stress, as used by the compute epair/atom, compute stress/atom, and dump custom commands, if all its sub-styles can perform per-atom calculations.

For the hybrid pair style, the list of sub-styles and their respective settings are written to binary restart files, so a pair_style command does not need to specified in an input script that reads a restart file. However, the coefficient information is not stored in the restart file. Thus, pair_coeff commands do need to be specified in the restart input script.

Restrictions:

A pair style of none can be specified as an argument to pair_style hybrid and the corresponding pair_coeff commands, if you desire to turn off pairwise interactions between certain pairs of atom types.

When using a long-range Coulomic solver (via the kspace_style command) with pair_style hybrid, one or more sub-styles will be of the "long" variety. E.g. lj/cut/coul/long or buck/coul/long. It is OK to have more than one sub-style with a "long" component, but you must insure that the short-range Coulombic cutoff used by each of these pair styles is consistent. Else the long-range Coulombic solve will be inconsistent.

Related commands:

pair_coeff

Default: none