forked from lijiext/lammps
178 lines
5.6 KiB
Plaintext
178 lines
5.6 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 class2 command :h3
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dihedral_style class2/omp command :h3
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[Syntax:]
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dihedral_style class2 :pre
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[Examples:]
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dihedral_style class2
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dihedral_coeff 1 100 75 100 70 80 60
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dihedral_coeff * mbt 3.5945 0.1704 -0.5490 1.5228
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dihedral_coeff * ebt 0.3417 0.3264 -0.9036 0.1368 0.0 -0.8080 1.0119 1.1010
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dihedral_coeff 2 at 0.0 -0.1850 -0.7963 -2.0220 0.0 -0.3991 110.2453 105.1270
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dihedral_coeff * aat -13.5271 110.2453 105.1270
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dihedral_coeff * bb13 0.0 1.0119 1.1010 :pre
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[Description:]
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The {class2} dihedral style uses the potential
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:c,image(Eqs/dihedral_class2.jpg)
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where Ed is the dihedral term, Embt is a middle-bond-torsion term,
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Eebt is an end-bond-torsion term, Eat is an angle-torsion term, Eaat
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is an angle-angle-torsion term, and Ebb13 is a bond-bond-13 term.
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Theta1 and theta2 are equilibrium angles and r1 r2 r3 are equilibrium
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bond lengths.
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See "(Sun)"_#Sun for a description of the COMPASS class2 force field.
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Coefficients for the Ed, Embt, Eebt, Eat, Eaat, and Ebb13 formulas
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must be defined for each dihedral type via the
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"dihedral_coeff"_dihedral_coeff.html command as in the example above,
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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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These are the 6 coefficients for the Ed formula:
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K1 (energy)
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phi1 (degrees)
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K2 (energy)
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phi2 (degrees)
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K3 (energy)
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phi3 (degrees) :ul
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For the Embt formula, each line in a
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"dihedral_coeff"_dihedral_coeff.html command in the input script lists
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5 coefficients, the first of which is "mbt" to indicate they are
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MiddleBondTorsion coefficients. In a data file, these coefficients
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should be listed under a "MiddleBondTorsion Coeffs" heading and you
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must leave out the "mbt", i.e. only list 4 coefficients after the
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dihedral type.
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mbt
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A1 (energy/distance)
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A2 (energy/distance)
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A3 (energy/distance)
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r2 (distance) :ul
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For the Eebt formula, each line in a
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"dihedral_coeff"_dihedral_coeff.html command in the input script lists
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9 coefficients, the first of which is "ebt" to indicate they are
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EndBondTorsion coefficients. In a data file, these coefficients
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should be listed under a "EndBondTorsion Coeffs" heading and you must
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leave out the "ebt", i.e. only list 8 coefficients after the dihedral
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type.
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ebt
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B1 (energy/distance)
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B2 (energy/distance)
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B3 (energy/distance)
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C1 (energy/distance)
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C2 (energy/distance)
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C3 (energy/distance)
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r1 (distance)
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r3 (distance) :ul
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For the Eat formula, each line in a
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"dihedral_coeff"_dihedral_coeff.html command in the input script lists
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9 coefficients, the first of which is "at" to indicate they are
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AngleTorsion coefficients. In a data file, these coefficients should
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be listed under a "AngleTorsion Coeffs" heading and you must leave out
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the "at", i.e. only list 8 coefficients after the dihedral type.
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at
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D1 (energy/radian)
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D2 (energy/radian)
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D3 (energy/radian)
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E1 (energy/radian)
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E2 (energy/radian)
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E3 (energy/radian)
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theta1 (degrees)
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theta2 (degrees) :ul
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Theta1 and theta2 are specified in degrees, but LAMMPS converts them
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to radians internally; hence the units of D and E are in
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energy/radian.
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For the Eaat formula, each line in a
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"dihedral_coeff"_dihedral_coeff.html command in the input script lists
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4 coefficients, the first of which is "aat" to indicate they are
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AngleAngleTorsion coefficients. In a data file, these coefficients
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should be listed under a "AngleAngleTorsion Coeffs" heading and you
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must leave out the "aat", i.e. only list 3 coefficients after the
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dihedral type.
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aat
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M (energy/radian^2)
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theta1 (degrees)
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theta2 (degrees) :ul
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Theta1 and theta2 are specified in degrees, but LAMMPS converts them
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to radians internally; hence the units of M are in energy/radian^2.
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For the Ebb13 formula, each line in a
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"dihedral_coeff"_dihedral_coeff.html command in the input script lists
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4 coefficients, the first of which is "bb13" to indicate they are
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BondBond13 coefficients. In a data file, these coefficients should be
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listed under a "BondBond13 Coeffs" heading and you must leave out the
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"bb13", i.e. only list 3 coefficients after the dihedral type.
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bb13
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N (energy/distance^2)
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r1 (distance)
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r3 (distance) :ul
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:line
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Styles with a {cuda}, {gpu}, {omp}, or {opt} suffix are functionally
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the same as the corresponding style without the suffix. They have
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been optimized to run faster, depending on your available hardware, as
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discussed in "Section_accelerate"_Section_accelerate.html of the
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manual. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
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packages, respectively. They are only enabled if LAMMPS was built with
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those packages. See the "Making LAMMPS"_Section_start.html#start_3
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section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the "-suffix command-line
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switch"_Section_start.html#start_7 when you invoke LAMMPS, or you can
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use the "suffix"_suffix.html command in your input script.
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See "Section_accelerate"_Section_accelerate.html of the manual for
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more instructions on how to use the accelerated styles effectively.
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:line
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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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CLASS2 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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[Default:] none
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:line
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:link(Sun)
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[(Sun)] Sun, J Phys Chem B 102, 7338-7364 (1998).
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