mirror of https://github.com/lammps/lammps.git
117 lines
4.2 KiB
Plaintext
Executable File
117 lines
4.2 KiB
Plaintext
Executable File
"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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pair_style gayberne command :h3
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[Syntax:]
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pair_style gayberne gamma upsilon mu cutoff :pre
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gamma = shift for potential minimum (typically 1)
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upsilon = exponent for eta orientation-dependent energy function
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mu = exponent for chi orientation-dependent energy function
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cutoff = global cutoff for interactions (distance units) :ul
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[Examples:]
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pair_style gayberne 1.0 1.0 1.0 10.0
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pair_coeff * * 1.0 1.7 1.7 3.4 3.4 1.0 1.0 1.0 :pre
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[Description:]
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Style {gayberne} computes a Gay-Berne anisotropic LJ interaction
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"(Beradi)"_#Beradi between pairs of ellipsoidal particles via the
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formulas
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:c,image(Eqs/pair_gayberne.jpg)
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where A1 and A2 are the transformation matrices from the simulation
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box frame to the body frame and r12 is the center to center vector
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between the particles. Ur controls the shifted distance dependent
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interaction based on the distance of closest approach of the two
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particles (h12) and the user-specified shift parameter gamma.
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For large uniform molecules it has been shown that the energy
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parameters are approximately representable in terms of local contact
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curvatures "(Everaers)"_#Everaers:
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:c,image(Eqs/pair_gayberne2.jpg)
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The variable names utilized as potential parameters are for the most
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part taken from "(Everaers)"_#Everaers in order to be consistent with
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its RE-squared potential fix. Details on the upsilon and mu
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parameters are given "here"_Eqs/pair_gayberne_extra.pdf.
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Use of this pair style requires the
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"fix nve/asphere"_fix_nve_asphere.html in order to integrate particle
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rotation. Additionally, "atom_style ellipsoid"_atom_style.html should
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be used since it defines the rotation state of the ellipsoidal
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particles.
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More details of the Gay-Berne formulation are given in the references
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listed below and in "this document"_Eqs/pair_gayberne_extra.pdf.
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The following coefficients must be defined for each pair of atoms
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types via the "pair_coeff"_pair_coeff.html command as in the examples
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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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epsilon = well depth (energy units)
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sigma = minimum effective particle radii (distance units)
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a = ellipsoid radius in x dimension (distance units)
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b = ellipsoid radius in y dimension (distance units)
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c = ellipsoid radius in z dimension (distance units)
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epsilon_a = relative well depth for side-to-side interactions
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epsilon_b = relative well depth for face-to-face interactions
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epsilon_c = relative well depth for end-to-end interactions
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cutoff (distance units) :ul
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The last coefficient is optional. If not specified, the global
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cutoff specified in the pair_style command is used.
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The epsilon and sigma parameters are mixed for I != J atom pairings
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the same as Lennard-Jones parameters; see the "pair_modify
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mix"_pair_modify.html documentation for details. The other parameters
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(except cutoff) are really specific to a single atom type, and not a
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pair of atoms. Thus they are applied to atom type I only.
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[Restrictions:]
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Can only be used if LAMMPS was built with the "asphere" package. Can
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only be used with "atom_style ellipsoid"_atom_style.html.
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The use of this potential requires additional fixes as described
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above. The "shift yes" option currently cannot be used with this
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potential to shift energies to 0 at the cutoff due to the anisotropic
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dependence of the interaction. Angular velocities are all set to zero
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initially. The Gay-Berne potential does not become isotropic as r
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increases "(Everaers)"_#Everaers. The distance of closest approach
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approximation becomes less accurate as the shape of ellipsoids becomes
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more dissimilar (high aspect ratio particles).
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[Related commands:]
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"pair_coeff"_pair_coeff.html, "fix nve/asphere"_fix_nve_asphere.html,
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"compute temp/asphere"_compute_temp_asphere.html
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[Default:] none
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:line
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:link(Everaers)
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[(Everaers)] Everaers and Ejtehadi, Phys Rev E, 67, 041710 (2003).
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:link(Berardi)
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[(Berardi)] Berardi, Fava, Zannoni, Chem Phys Lett, 297, 8-14 (1998).
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:link(Perram)
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[(Perram)] Perram and Rasmussen, Phys Rev E, 54, 6565-6572 (1996).
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:link(Allen)
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[(Allen)] Allen and Germano, Mol Phys 104, 3225-3235 (2006).
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