forked from lijiext/lammps
61 lines
1.7 KiB
Plaintext
61 lines
1.7 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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dihedral_style cosine/shift/exp command :h3
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[Syntax:]
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dihedral_style cosine/shift/exp :pre
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[Examples:]
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dihedral_style cosine/shift/exp
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dihedral_coeff 1 10.0 45.0 2.0 :pre
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[Description:]
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The {cosine/shift/exp} dihedral style uses the potential
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:c,image(Eqs/dihedral_cosine_shift_exp.jpg)
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where Umin, theta, and a are defined for each dihedral type.
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The potential is bounded between \[-Umin:0\] and the minimum is located
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at the angle theta0. The a parameter can be both positive or negative
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and is used to control the spring constant at the equilibrium.
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The spring constant is given by k=a exp(a) Umin/ \[2 (Exp(a)-1)\].
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For a>3 k/Umin = a/2 to better than 5% relative error. For negative
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values of the a parameter, the spring constant is essentially zero,
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and anharmonic terms takes over. The potential is furthermore well
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behaved in the limit a->0, where it has been implemented to linear
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order in a for a < 0.001.
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The following coefficients must be defined for each dihedral type via
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the "dihedral_coeff"_dihedral_coeff.html command as in the example
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above, or in the data file or restart files read by the
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"read_data"_read_data.html or "read_restart"_read_restart.html
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commands:
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umin (energy)
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theta (angle)
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A (real number) :ul
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[Restrictions:]
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This dihedral style can only be used if LAMMPS was built with the
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USER-MISC package. See the "Making LAMMPS"_Section_start.html#start_3
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section for more info on packages.
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[Related commands:]
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"dihedral_coeff"_dihedral_coeff.html,
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"angle_cosineshiftexp"_angle_cosineshiftexp.html
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[Default:] none
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