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angle_style command

Syntax:

angle_style style 

Examples:

angle_style harmonic
angle_style charmm
angle_style hybrid harmonic cosine 

Description:

Set the formula(s0 LAMMPS will use to compute angle interactions between triplets of atoms. The list of atom triplets is specified in the data or restart file and is read in by a read_data or read_restart command. The coefficients for the formula for each angle type can also be specified in those files or via the angle_coeff command. In all the formulas to follow, theta is the angle defined by the triplet of aotms.

A style of none means angle forces are not computed, even if angles are defined.


The charmm style uses the potential

with an additional Urey_Bradley term based on the distance r between the 1st and 3rd atoms in the angle. K, theta0, Kub, and Rub are coefficients defined for each angle type.


The class2 style uses the potential

where Ea is the angle term, Ebb is a bond-bond term, and Eba is a bond-angle term. Theta0 is the equilibrium angle and r1 and r2 are the equilibrium bond lengths. Kn, M, Nn, theta0, r1, r2 are coefficients defined for each angle type.


The cosine style uses the potential

where K is defined for each angle type.


The cosine/squared style is a potential commonly used in the Gromacs MD code and is of the form

where theta0 is the equilibrium value of the angle, and K is a prefactor. Note that the usual 1/2 factor is included in K. K and theta0 are coefficients defined for each angle type.


The harmonic style uses the potential

where theta0 is the equilibrium value of the angle, and K is a prefactor. Note that the usual 1/2 factor is included in K. K and theta0 are coefficients defined for each angle type.


The hybrid style enables the use of multiple angle styles in one simulation. An angle style is assigned to each angle type. For example, angles in a polymer flow (of angle type 1) could be computed with a cosine potential and angles in the wall boundary (of angle type 2) could be computed with a harmonic potential. The assignment of angle type to style is made via the angle_coeff command or in the data file.


Restrictions:

Angle styles can only be set for atom_styles that allow angles to be defined.

Angle styles are part of the "molecular" package. They are only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.

Related commands:

angle_coeff

Default:

angle_style none