\(\renewcommand{\AA}{\text{Å}}\)

bond_style bpm/zero command

Syntax

bond_style bpm/zero keyword value attribute1 attribute2 ...

zero or more keyword/value pairs may be appended

keyword = manybody or overlay/pair or break or store/local

manybody value = yes or no
   exercise the per-atom multibody communication machinery

overlay/pair value = yes or no
   bonded particles will still interact with pair forces

break value = yes or no
   indicates whether bonds break during a run

store/local values = fix_ID N attributes ...
   (as for bond_style bpm/spring)

Examples

bond_style bpm/zero
bond_coeff 1 0.1

bond_style bpm/zero break no
bond_coeff 1 0.0

Description

Added in version TBD.

The bpm/zero bond style is the BPM analogue of bond_style zero: it stores the initial reference state of each bond and can break bonds individually, but it computes no bond force or energy. Like the other BPM bond styles the reference length is recorded when a bond is first computed in the setup of a run, is preserved across run commands, and is written to binary restart files.

A bond breaks when its strain \((r - r_0)/r_0\) exceeds the critical value \(\epsilon_c\) given by bond_coeff (unless break is set to no). Because no force is applied, broken or unbroken the particles move only under the other forces in the system.

This style is intended for testing, debugging, and as a starting template, not for production mechanics. Useful cases include:

exercising the BPM bond infrastructure — reference-state storage, individual bond breaking, per-bond history, broken-bond output via store/local, and (with manybody yes) the per-atom forward/reverse communication used by multibody BPM styles — without a specific constitutive law;
holding a fixed bond topology (for example for connectivity or special_bonds bookkeeping) without bond forces;
serving as a minimal template when implementing a new BPM bond style.

The following coefficient must be defined for each bond type via the bond_coeff command:

\(\epsilon_c\) (unitless), critical strain for breaking

The manybody keyword toggles an internal per-atom property and its forward/reverse communication so the multibody machinery shared by the BPM styles can be exercised in isolation. The overlay/pair, break, and store/local keywords behave as for bond_style bpm/spring; see the BPM Howto.

Restart and other info

This bond style writes the reference state of each bond to binary restart files. The reference state is not written to data files. If store/local is used, an internal fix records broken-bond data accessible through a dump local command, as for the other BPM bond styles.

Restrictions

This bond 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.

As with the other BPM bond styles, newton must be set to bond off and the special bond weights must be

special_bonds lj 0 1 1 coul 1 1 1

(or all weights one with overlay/pair yes).

Default

The option default is manybody = no (plus the BPM defaults overlay/pair = no, break = yes).