pair_style bpm/peri command
Accelerator Variants: bpm/peri/omp
Syntax
pair_style bpm/peri
Examples
pair_style bpm/peri
pair_coeff * * 1.6863e22 0.0015001
Description
Added in version 2Sep2026.
Style bpm/peri supplies the short-range repulsive contact force between non-bonded peridynamic nodes for the bond_style bpm/peri model. It is the BPM-framework equivalent of the contact term built into the legacy peridynamic pair styles. Bonded pairs are handled entirely by the bond style and are excluded here through the 1-2 special_bonds weight; this pair style therefore acts only between nodes that are not bonded (for example new contacts that form after fracture or large deformation).
For a pair of non-bonded nodes within the contact distance \(d = 1.35\, l_c\) (where \(l_c\) is the lattice spacing) the force has magnitude
where k is the contact stiffness, \(\delta\) the horizon, \(r\) the current distance, and \(\bar{V} = (V_i + V_j)/2\) the mean nodal volume of the two nodes (read from the per-atom vfrac property declared for the bond style). The factor 15 follows the EMU Theory Manual convention used by the legacy peridynamic styles.
The following coefficients must be defined for each pair of atom types via the pair_coeff command as in the example above, or in the restart files read by the read_restart command:
k (energy/distance/volume^2 units), contact stiffness
horizon \(\delta\) (distance units)
Typically k and the horizon are set equal to the corresponding bond_coeff values.
Styles with a gpu, intel, kk, omp, or opt suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed on the Accelerator packages page. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues.
These accelerated styles are part of the GPU, INTEL, KOKKOS, OPENMP, and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Build package page for more info.
You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the -suffix command-line switch when you invoke LAMMPS, or you can use the suffix command in your input script.
See the Accelerator packages page for more instructions on how to use the accelerated styles effectively.
Mixing, shift, table, tail correction, restart, rRESPA info
This pair style does not support mixing. Coefficients for all I,J pairs must be specified explicitly.
This pair style does not support the pair_modify shift, table, or tail options.
This pair style writes its information to binary restart files, so pair_style and pair_coeff commands do not need to be specified in an input script that reads a restart file.
This pair style can only be used via the pair keyword of the run_style respa command. It does not support the inner, middle, outer keywords.
Restrictions
This pair style is part of the BPM package. It is only enabled if LAMMPS was built with that package. See the Build package page for more info.
This pair style requires a per-atom vfrac property (a fix property/atom d_vfrac with ghost communication) and a cubic lattice with equal spacing in x, y, and z. It is intended to be used together with bond_style bpm/peri. See the peridynamics Howto.
Default
none