Syntax:
dihedral_style style
Examples:
dihedral_style harmonic dihedral_style multiharmonic
Description:
Set the formula LAMMPS will use to compute dihedral interactions between quadruplets of atoms. The list of atom quadruplets 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 dihedral type can also be specified in those files or by the dihedral_coeff command. In all the formulas to follow, phi is the torsional angle defined by the quadruplet of atoms.
Here are some important points to take note of when defining the LAMMPS dihedral coefficients in the formulas that follow so that they are compatible with other force fields:
A style of none means dihedral forces are not computed, even if dihedrals are defined.
The charmm style uses the potential
K, d, and n are coefficients defined for each dihedral type. Additionally, a weighting factor if defined (see the dihedral_coeff command) which is applied to the pairwise LJ and Coulombic interaction between the 1st and 4th atom in the dihedral quadruplet.
The class2 style uses the potential
where Ed is the dihedral term, Embt is a middle-bond-torsion term, Eebt is an end-bond-torsion term, Eat is an angle-torsion term, Eaat is an angle-angle-torsion term, and Ebb13 is a bond-bond-13 term.
Theta1 and theta2 are equilibrium angles and r1 r2 r3 are equilibrium bond lengths. Kn, An, Bn, Cn, Dn, En, M, N, Phi_n, theta1, theta2, r1, r2, r3 are coefficients defined for each dihedral type.
The harmonic style uses the potential
K, d, and n are coefficients defined for each dihedral type.
The multiharmonic style uses the potential
A1, A2, A3, A4, and A5 are coefficients defined for each dihedral type.
Restrictions:
Dihedral styles can only be set for atom styles that allow dihedrals to be defined.
Dihedral 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:
Default:
dihedral_style none