style = none or hybrid or charmm or class2 or cosine or cosine/squared or harmonic
angle_style harmonic angle_style charmm angle_style hybrid harmonic cosine
Set the formula(s) LAMMPS uses to compute angle interactions between triplets of atoms, which remain in force for the duration of the simulation. The list of angle triplets is read in by a read_data or read_restart command from a data or restart file.
Hybrid models where angles are computed using different angle potentials can be setup using the hybrid angle style.
The coefficients associated with a angle style can be specified in a data or restart file or via the angle_coeff command.
All angle potentials store their coefficient data in binary restart files which means angle_style and angle_coeff commands do not need to be re-specified in an input script that restarts a simulation. See the read_restart command for details on how to do this. The one exception is that angle_style hybrid only stores the list of sub-styles in the restart file; angle coefficients need to be re-specified.
When both an angle and pair style is defined, the special_bonds command often needs to be used to turn off (or weight) the pairwise interaction that would otherwise exist between 3 bonded atoms.
In the formulas listed for each angle style, theta is the angle between the 3 atoms in the angle.
Here is an alphabetic list of angle styles defined in LAMMPS. Click on the style to display the formula it computes and coefficients specified by the associated angle_coeff command.
Click on the style to display the formula it computes, any additional arguments specified in the angle_style command, and coefficients specified by the associated angle_coeff command.
There are also additional accelerated pair styles included in the LAMMPS distribution for faster performance on CPUs, GPUs, and KNLs. The individual style names on the Commands angle doc page are followed by one or more of (g,i,k,o,t) to indicate which accelerated styles exist.
none - turn off angle interactions
zero - topology but no interactions
hybrid - define multiple styles of angle interactions
charmm - CHARMM angle
class2 - COMPASS (class 2) angle
class2/p6 - COMPASS (class 2) angle expanded to 6th order
cosine - angle with cosine term
cosine/buck6d - same as cosine with Buckingham term between 1-3 atoms
cosine/delta - angle with difference of cosines
cosine/periodic - DREIDING angle
cosine/shift - angle cosine with a shift
cosine/shift/exp - cosine with shift and exponential term in spring constant
cosine/squared - angle with cosine squared term
cross - cross term coupling angle and bond lengths
dipole - angle that controls orientation of a point dipole
fourier - angle with multiple cosine terms
fourier/simple - angle with a single cosine term
gaussian - multicentered Gaussian-based angle potential
harmonic - harmonic angle
mm3 - anharmonic angle
quartic - angle with cubic and quartic terms
sdk - harmonic angle with repulsive SDK pair style between 1-3 atoms
table - tabulated by angle
Angle styles can only be set for atom_styles that allow angles to be defined.
Most angle styles are part of the MOLECULE package. They are only enabled if LAMMPS was built with that package. See the Build package doc page for more info. The doc pages for individual bond potentials tell if it is part of a package.