"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

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angle_style dipole command :h3
angle_style dipole/omp command :h3

[Syntax:]

angle_style dipole :pre

[Examples:]

angle_style dipole
angle_coeff 6 2.1 180.0 :pre

[Description:]

The {dipole} angle style is used to control the orientation of a dipolar
atom within a molecule "(Orsi)"_#Orsi. Specifically, the {dipole} angle 
style restrains the orientation of a point dipole mu_j (embedded in atom 
'j') with respect to a reference (bond) vector r_ij = r_i - r_j, where 'i' 
is another atom of the same molecule (typically, 'i' and 'j' are also 
covalently bonded). 

It is convenient to define an angle gamma between the 'free' vector mu_j
and the reference (bond) vector r_ij:

:c,image(Eqs/angle_dipole_gamma.jpg)

The {dipole} angle style uses the potential:

:c,image(Eqs/angle_dipole_potential.jpg)

where K is a rigidity constant and gamma0 is an equilibrium (reference)
angle. 

The torque on the dipole can be obtained by differentiating the 
potential using the 'chain rule' as in appendix C.3 of 
"(Allen)"_#Allen:

:c,image(Eqs/angle_dipole_torque.jpg)

Example: if gamma0 is set to 0 degrees, the torque generated by
the potential will tend to align the dipole along the reference 
direction defined by the (bond) vector r_ij (in other words, mu_j is
restrained to point towards atom 'i').

Note that the angle dipole potential does not give rise to any force, 
because it does not depend on the distance between i and j (it only 
depends on the angle between mu_j and r_ij).

The following coefficients must be defined for each angle type via the
"angle_coeff"_angle_coeff.html command as in the example above, or in
the data file or restart files read by the "read_data"_read_data.html
or "read_restart"_read_restart.html commands:

K (energy)
gamma0 (degrees) :ul

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Styles with a {cuda}, {gpu}, {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 in "Section_accelerate"_Section_accelerate.html of the
manual.  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 USER-CUDA, GPU, USER-OMP and OPT
packages, respectively.  They are only enabled if LAMMPS was built with
those packages.  See the "Making LAMMPS"_Section_start.html#start_3
section 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"_Section_start.html#start_6 when you invoke LAMMPS, or you can
use the "suffix"_suffix.html command in your input script.

See "Section_accelerate"_Section_accelerate.html of the manual for
more instructions on how to use the accelerated styles effectively.

[Restrictions:]

This angle style can only be used if LAMMPS was built with the
USER-MISC package.  See the "Making LAMMPS"_Section_start.html#2_3
section for more info on packages.

IMPORTANT NOTE: In the "Angles" section of the data file, the atom ID
'j' corresponding to the dipole to restrain must come before the atom
ID of the reference atom 'i'. A third atom ID 'k' must also be
provided, although 'k' is just a 'dummy' atom which can be any atom;
it may be useful to choose a convention (e.g., 'k'='i') and adhere to
it.  For example, if ID=1 for the dipolar atom to restrain, and ID=2
for the reference atom, the corresponding line in the "Angles" section
of the data file would read: X X 1 2 2

The "newton" command for intramolecular interactions must be "on"
(which is the default).

This angle style should not be used with SHAKE.

[Related commands:]

"angle_coeff"_angle_coeff.html, "angle_hybrid"_angle_hybrid.html

[Default:] none

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:link(Orsi)
[(Orsi)] Orsi & Essex, The ELBA force field for coarse-grain modeling of 
lipid membranes, PloS ONE 6(12): e28637, 2011.

:link(Allen)
[(Allen)] Allen & Tildesley, Computer Simulation of Liquids,
Clarendon Press, Oxford, 1987.
