forked from lijiext/lammps
97 lines
3.4 KiB
Plaintext
97 lines
3.4 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,Commands_all.html)
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:line
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dihedral_coeff command :h3
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[Syntax:]
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dihedral_coeff N args :pre
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N = dihedral type (see asterisk form below)
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args = coefficients for one or more dihedral types :ul
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[Examples:]
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dihedral_coeff 1 80.0 1 3
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dihedral_coeff * 80.0 1 3 0.5
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dihedral_coeff 2* 80.0 1 3 0.5 :pre
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[Description:]
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Specify the dihedral force field coefficients for one or more dihedral types.
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The number and meaning of the coefficients depends on the dihedral style.
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Dihedral coefficients can also be set in the data file read by the
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"read_data"_read_data.html command or in a restart file.
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N can be specified in one of two ways. An explicit numeric value can
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be used, as in the 1st example above. Or a wild-card asterisk can be
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used to set the coefficients for multiple dihedral types. This takes the
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form "*" or "*n" or "n*" or "m*n". If N = the number of dihedral types,
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then an asterisk with no numeric values means all types from 1 to N. A
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leading asterisk means all types from 1 to n (inclusive). A trailing
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asterisk means all types from n to N (inclusive). A middle asterisk
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means all types from m to n (inclusive).
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Note that using a dihedral_coeff command can override a previous setting
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for the same dihedral type. For example, these commands set the coeffs
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for all dihedral types, then overwrite the coeffs for just dihedral type 2:
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dihedral_coeff * 80.0 1 3
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dihedral_coeff 2 200.0 1 3 :pre
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A line in a data file that specifies dihedral coefficients uses the exact
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same format as the arguments of the dihedral_coeff command in an input
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script, except that wild-card asterisks should not be used since
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coefficients for all N types must be listed in the file. For example,
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under the "Dihedral Coeffs" section of a data file, the line that
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corresponds to the 1st example above would be listed as
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1 80.0 1 3 :pre
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The "dihedral_style class2"_dihedral_class2.html is an exception to
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this rule, in that an additional argument is used in the input script
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to allow specification of the cross-term coefficients. See its doc
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page for details.
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NOTE: When comparing the formulas and coefficients for various LAMMPS
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dihedral styles with dihedral equations defined by other force fields,
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note that some force field implementations divide/multiply the energy
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prefactor {K} by the multiple number of torsions that contain the J-K
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bond in an I-J-K-L torsion. LAMMPS does not do this, i.e. the listed
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dihedral equation applies to each individual dihedral. Thus you need
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to define {K} appropriately to account for this difference if
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necessary.
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:line
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The list of all dihedral styles defined in LAMMPS is given on the
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"dihedral_style"_dihedral_style.html doc page. They are also listed
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in more compact form on the "Commands
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dihedral"_Commands_bond.html#dihedral doc page.
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On either of those pages, click on the style to display the formula it
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computes and its coefficients as specified by the associated
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dihedral_coeff command.
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:line
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[Restrictions:]
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This command must come after the simulation box is defined by a
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"read_data"_read_data.html, "read_restart"_read_restart.html, or
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"create_box"_create_box.html command.
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A dihedral style must be defined before any dihedral coefficients are
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set, either in the input script or in a data file.
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[Related commands:]
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"dihedral_style"_dihedral_style.html
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[Default:] none
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