forked from lijiext/lammps
127 lines
4.4 KiB
Plaintext
127 lines
4.4 KiB
Plaintext
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"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 thole command :h3
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[Syntax:]
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pair_style thole damp cutoff :pre
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thole = style name
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damp = global damping parameter
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cutoff = global cutoff :ul
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[Examples:]
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pair_style hybrid/overlay ... thole 2.6 12.0
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pair_coeff 1 1 thole 1.0
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pair_coeff 1 2 thole 1.0 2.6 10.0
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pair_coeff * 2 thole 1.0 2.6 :pre
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[Description:]
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The {thole} pair style is meant to be used with force fields that
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include explicit polarization through Drude dipoles. This link
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describes how to use the "thermalized Drude oscillator
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model"_tutorial_drude.html in LAMMPS and polarizable models in LAMMPS
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are discussed in "this Section"_Section_howto.html#howto_25.
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The {thole} pair style should be used as a sub-style within in the
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"pair_hybrid/overlay"_pair_hybrid.html command, in conjunction with a
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main pair style including Coulomb interactions, i.e. any pair style
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containing {coul/cut} or {coul/long} in its style name.
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The {thole} pair style computes the Coulomb interaction damped at
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short distances by a function
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\begin\{equation\} T_\{ij\}(r_\{ij\}) = 1 - \left( 1 +
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\frac\{s_\{ij\} r_\{ij\} \}\{2\} \right)
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\exp \left( - s_\{ij\} r_\{ij\} \right) \end\{equation\}
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This function results from an adaptation to point charges
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"(Noskov)"_#Noskov of the dipole screening scheme originally proposed
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by "Thole"_#Thole. The scaling coefficient \(s_\{ij\} \) is determined
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by the polarizability of the atoms, \( \alpha_i \), and by a Thole
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damping parameter \( a \). This Thole damping parameter usually takes
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a value of 2.6, but in certain force fields the value can depend upon
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the atom types. The mixing rule for Thole damping parameters is the
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arithmetic average, and for polarizabilities the geometric average
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between the atom-specific values.
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\begin\{equation\} s_\{ij\} = \frac\{ a_\{ij\} \}\{
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(\alpha_\{ij\})^\{1/3\} \} = \frac\{ (a_i + a_j)/2 \}\{
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\[(\alpha_i\alpha_j)^\{1/2\}\]^\{1/3\} \} \end\{equation\}
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The damping function is only applied to the interactions between the
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point charges representing the induced dipoles on polarizable sites,
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that is, charges on Drude particles, \( q_\{D,i\} \), and opposite
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charges, \( -q_\{D,i\} \), located on the respective core particles
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(to which each Drude particle is bonded). Therefore, Thole screening
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is not applied to the full charge of the core particle \( q_i \), but
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only to the \( -q_\{D,i\} \) part of it.
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The interactions between core charges are subject to the weighting
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factors set by the "special_bonds"_special_bonds.html command. The
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interactions between Drude particles and core charges or
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non-polarizable atoms are also subject to these weighting factors. The
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Drude particles inherit the 1-2, 1-3 and 1-4 neighbor relations from
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their respective cores.
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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 example
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above.
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alpha (distance units^3)
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damp
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cutoff (distance units) :ul
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The last two coefficients are optional. If not specified the global
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Thole damping parameter or global cutoff specified in the pair_style
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command are used. In order to specify a cutoff (third argument) a damp
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parameter (second argument) must also be specified.
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[Mixing]:
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The {thole} pair style does not support mixing. Thus, coefficients
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for all I,J pairs must be specified explicitly.
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[Restrictions:]
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These pair styles are part of the USER-DRUDE package. They are only
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enabled if LAMMPS was built with that package. See the "Making
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LAMMPS"_Section_start.html#start_3 section for more info.
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This pair_style should currently not be used with the "charmm dihedral
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style"_dihedral_charmm.html if the latter has non-zero 1-4 weighting
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factors. This is because the {thole} pair style does not know which
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pairs are 1-4 partners of which dihedrals.
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[Related commands:]
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"fix drude"_fix_drude.html, "fix
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langevin/drude"_fix_langevin_drude.html, "fix
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drude/transform"_fix_drude_transform.html, "compute
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temp/drude"_compute_temp_drude.html
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[Default:] none
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:line
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:link(Noskov)
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[(Noskov)] Noskov, Lamoureux and Roux, J Phys Chem B, 109, 6705 (2005).
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:link(Thole)
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[(Thole)] Chem Phys, 59, 341 (1981).
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