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documenting bpm multibody

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jtclemm
2024-10-21 15:07:06 -06:00
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doc/src/bond_bpm_spring.rst
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@ -10,7 +10,7 @@ Syntax
bond_style bpm/spring keyword value attribute1 attribute2 ...
* optional keyword = *overlay/pair* or *store/local* or *smooth* or *break*
* optional keyword = *overlay/pair* or *store/local* or *smooth* or *break* or *volume/factor*
.. parsed-literal::
@ -36,6 +36,9 @@ Syntax
*break* value = *yes* or *no*
indicates whether bonds break during a run
*volume/factor* value = *yes* or *no*
indicates whether forces include the volumetric contribution
Examples
""""""""
@ -44,6 +47,9 @@ Examples
bond_style bpm/spring
bond_coeff 1 1.0 0.05 0.1
bond_style bpm/spring volume/factor yes
bond_coeff 1 1.0 0.05 0.1 0.5
bond_style bpm/spring myfix 1000 time id1 id2
dump 1 all local 1000 dump.broken f_myfix[1] f_myfix[2] f_myfix[3]
dump_modify 1 write_header no
@ -97,15 +103,6 @@ approach the critical strain
w = 1.0 - \left( \frac{r - r_0}{r_0 \epsilon_c} \right)^8 .
The following coefficients must be defined for each bond type via the
:doc:`bond_coeff <bond_coeff>` command as in the example above, or in
the data file or restart files read by the :doc:`read_data
<read_data>` or :doc:`read_restart <read_restart>` commands:
* :math:`k` (force/distance units)
* :math:`\epsilon_c` (unit less)
* :math:`\gamma` (force/velocity units)
If the *normalize* keyword is set to *yes*, the elastic bond force will be
normalized by :math:`r_0` such that :math:`k` must be given in force units.
@ -123,6 +120,43 @@ during a simulation run. This will prevent some unnecessary calculation.
However, if a bond reaches a strain greater than :math:`\epsilon_c`,
it will trigger an error.
.. versionadded:: TBD
The *volume/factor* keyword toggles whether an additional multibody
contribution is added to he force using the formulation in
:ref:`(Clemmer2) <multibody-Clemmer>`,
.. math::
\alpha_v \left(\left[\frac{V_i + V_j}{V_{0,i} + V_{0,j}}\right]^{1/3} - \frac{r_{ij}}{r_{0,ij}}\right)
where :math:`\alpha_v` is a user specified coefficient and :math:`V_i`
and :math:`V_{0,i}` are estimates of the current and local volume
of atom :math:`i`. These volumes are calculated as the sum of current
or initial bond lengths cubed. In 2D, the volume is replaced with an area
calculated using bond lengths squared and the cube root in the above equation
is accordingly replaced with a square root. This approximation assumes bonds
are evenly distributed on a spherical surface and neglects constant prefactors
which are irrelevant since only the ratio of volumes matters. This term may be
used to adjust the Poisson's ratio.
If a bond is broken (or created), :math:`V_{0,i}` is updated by subtracting
(or adding) that bond's contribution.
The following coefficients must be defined for each bond type via the
:doc:`bond_coeff <bond_coeff>` command as in the example above, or in
the data file or restart files read by the :doc:`read_data
<read_data>` or :doc:`read_restart <read_restart>` commands:
* :math:`k` (force/distance units)
* :math:`\epsilon_c` (unit less)
* :math:`\gamma` (force/velocity units)
Additionally, if *volume/factor* is set to *yes*, a fourth coefficient
must be provided:
* :math:`a_v` (force units)
If the *store/local* keyword is used, an internal fix will track bonds that
break during the simulation. Whenever a bond breaks, data is processed
and transferred to an internal fix labeled *fix_ID*. This allows the
@ -213,7 +247,7 @@ Related commands
Default
"""""""
The option defaults are *overlay/pair* = *no*, *smooth* = *yes*, *normalize* = *no*, and *break* = *yes*
The option defaults are *overlay/pair* = *no*, *smooth* = *yes*, *normalize* = *no*, *break* = *yes*, and *volume/factor* = *no*
----------
@ -224,3 +258,7 @@ The option defaults are *overlay/pair* = *no*, *smooth* = *yes*, *normalize* = *
.. _Groot4:
**(Groot)** Groot and Warren, J Chem Phys, 107, 4423-35 (1997).
.. _multibody-Clemmer:
**(Clemmer2)** Clemmer, Monti, Lechman, Soft Matter, 20, 1702 (2024).