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dihedral_style spherical command

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Syntax

+
dihedral_style spherical
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Examples

+
dihedral_coeff 1 1  286.1  1 124 1   1 90.0 0   1 90.0 0
+dihedral_coeff 1 3  286.1  1 114 1   1 90  0    1 90.0  0  &
+                    17.3   0 0.0 0   1 158 1    0 0.0   0  &
+                    15.1   0 0.0 0   0 0.0 0    1 167.3 1
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Description

+

The spherical dihedral style uses the potential:

+_images/dihedral_spherical_angles.jpg +_images/dihedral_spherical.jpg +

For this dihedral style, the energy can be any function that combines the +4-body dihedral-angle (phi) and the two 3-body bond-angles (theta1, theta2). +For this reason, there is usually no need to define 3-body “angle” forces +separately for the atoms participating in these interactions. +It is probably more efficient to incorporate 3-body angle forces into +the dihedral interaction even if it requires adding additional terms to +the expansion (as was done in the second example). A careful choice of +parameters can prevent singularities that occur with traditional +force-fields whenever theta1 or theta2 approach 0 or 180 degrees. +The last example above corresponds to an interaction with a single energy +minima located at phi=114, theta1=158, theta2=167.3 degrees, and it remains +numerically stable at all angles (phi, theta1, theta2). In this example, +the coefficients 17.3, and 15.1 can be physically interpreted as the +harmonic spring constants for theta1 and theta2 around their minima. +The coefficient 286.1 is the harmonic spring constant for phi after +division by sin(158)*sin(167.3) (the minima positions for theta1 and theta2).

+

The following coefficients must be defined for each dihedral type via the +dihedral_coeff command as in the example above, or in +the Dihedral Coeffs section of a data file file read by the +read_data command:

+
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  • n (integer >= 1)
    • +
  • C1 (energy)
    • +
  • K1 (typically an integer)
    • +
  • a1 (degrees)
    • +
  • u1 (typically 0.0 or 1.0)
    • +
  • L1 (typically an integer)
    • +
  • b1 (degrees, typically 0.0 or 90.0)
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  • v1 (typically 0.0 or 1.0)
    • +
  • M1 (typically an integer)
    • +
  • c1 (degrees, typically 0.0 or 90.0)
    • +
  • w1 (typically 0.0 or 1.0)
    • +
  • +
  • Cn (energy)
    • +
  • Kn (typically an integer)
    • +
  • an (degrees)
    • +
  • un (typically 0.0 or 1.0)
    • +
  • Ln (typically an integer)
    • +
  • bn (degrees, typically 0.0 or 90.0)
    • +
  • vn (typically 0.0 or 1.0)
    • +
  • Mn (typically an integer)
    • +
  • cn (degrees, typically 0.0 or 90.0)
    • +
  • wn (typically 0.0 or 1.0)
    • +
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Restrictions

+

This dihedral style can only be used if LAMMPS was built with the +USER_MISC package. See the Making LAMMPS +section for more info on packages.

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