Syntax:
fix ID group-ID qeq/reax Nevery cutlo cuthi tolerance params
Examples:
fix 1 all qeq/reax 1 0.0 10.0 1.0e-6 reax/c fix 1 all qeq/reax 1 0.0 10.0 1.0e-6 param.qeq
Description:
Perform the charge equilibration (QEq) method as described in (Rappe and Goddard, 1991) and formulated in (Nakano, 1997). It is typically used in conjunction with the ReaxFF force field model as implemented in the pair_style reax/c command.
The QEq method minimizes the electrostatic energy of the system by adjusting the partial charge on individual atoms based on interactions with their neighbors. It reqires some parameters for each atom type. If the params setting above is the word "reax/c", then these are extracted from the pair_style reax/c command and the ReaxFF force field file it reads in. If a file name is specified for params, then the parameters are taken from the specified file and the file must contain one line for each atom type. Each line should be formatted as follows:
itype chi eta gamma
where itype is the atom type from 1 to Ntypes, chi denotes the electronegativity in energy units, eta denotes the self-Coulomb potential in energy units, and gamma denotes the valence orbital exponent. Note that these 3 quantities are also in the ReaxFF potential file, except that eta is defined here as twice the eta value in the ReaxFF file.
Restart, fix_modify, output, run start/stop, minimize info:
No information about this fix is written to binary restart files. No global scalar or vector or per-atom quantities are stored by this fix for access by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command.
This fix is invoked during energy minimization.
Restrictions:
This fix is part of the "user-reaxc" package. It is only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.
Related commands:
Default: none
(Rappe) Rappe and Goddard III, Journal of Physical Chemistry, 105, 3358-3363 (1991).
(Nakano) Nakano, Computer Physics Communications, 104, 59-69 (1997).