forked from lijiext/lammps
129 lines
4.6 KiB
Plaintext
129 lines
4.6 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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kspace_style command :h3
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[Syntax:]
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kspace_style style value :pre
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style = {none} or {ewald} or {pppm} or {pppm/tip4p} or {ewald/n} :ulb,l
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{none} value = none
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{ewald} value = precision
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precision = desired accuracy
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{pppm} value = precision
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precision = desired accuracy
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{pppm/tip4p} value = precision
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precision = desired accuracy
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{ewald/n} value = precision
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precision = desired accuracy :pre
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:ule
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[Examples:]
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kspace_style pppm 1.0e-4
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kspace_style none :pre
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[Description:]
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Define a K-space solver for LAMMPS to use each timestep to compute
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long-range Coulombic interactions or long-range 1/r^N interactions.
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When such a solver is used in conjunction with an appropriate pair
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style, the cutoff for Coulombic or other 1/r^N interactions is
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effectively infinite; each charge in the system interacts with charges
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in an infinite array of periodic images of the simulation domain.
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The {ewald} style performs a standard Ewald summation as described in
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any solid-state physics text.
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The {pppm} style invokes a particle-particle particle-mesh solver
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"(Hockney)"_#Hockney which maps atom charge to a 3d mesh, uses 3d FFTs
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to solve Poisson's equation on the mesh, then interpolates electric
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fields on the mesh points back to the atoms. It is closely related to
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the particle-mesh Ewald technique (PME) "(Darden)"_#Darden used in
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AMBER and CHARMM. The cost of traditional Ewald summation scales as
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N^(3/2) where N is the number of atoms in the system. The PPPM solver
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scales as Nlog(N) due to the FFTs, so it is almost always a faster
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choice "(Pollock)"_#Pollock.
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The {pppm/tip4p} style is identical to the {pppm} style except that it
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adds a charge at the massless 4th site in each TIP4P water molecule.
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It should be used with "pair styles"_pair_style.html with a
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{long/tip4p} in their style name.
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The {ewald/n} style augments {ewald} by adding long-range dispersion
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sum capabilities for 1/r^N potentials and is useful for simulation of
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interfaces "(Veld)"_#Veld. It also performs standard coulombic Ewald
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summations, but in a more efficient manner than the {ewald} style.
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The 1/r^N capability means that Lennard-Jones or Buckingham potentials
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can be used with {ewald/n} without a cutoff, i.e. they become full
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long-range potentials.
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Currently, only the {ewald/n} style can be used with non-orthogonal
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(triclinic symmetry) simulation boxes.
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When a kspace style is used, a pair style that includes the
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short-range correction to the pairwise Coulombic or other 1/r^N forces
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must also be selected. For Coulombic interactions, these styles are
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ones that have a {coul/long} in their style name. For 1/r^6
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dispersion forces in a Lennard-Jones or Buckingham potential, see the
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"pair_style lj/coul"_pair_lj_coul.html or "pair_style
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buck/coul"_pair_buck_coul.html commands.
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A precision value of 1.0e-4 means one part in 10000. This setting is
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used in conjunction with the pairwise cutoff to determine the number
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of K-space vectors for style {ewald} or the FFT grid size for style
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{pppm}.
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See the "kspace_modify"_kspace_modify.html command for additional
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options of the K-space solvers that can be set.
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[Restrictions:]
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A simulation must be 3d and periodic in all dimensions to use an Ewald
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or PPPM solver. The only exception is if the slab option is set with
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"kspace_modify"_kspace_modify.html, in which case the xy dimensions
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must be periodic and the z dimension must be non-periodic.
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Kspace styles are part of the "kspace" package. They are only enabled
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if LAMMPS was built with that package. See the "Making
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LAMMPS"_Section_start.html#2_3 section for more info.
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The {ewald/n} style is part of the "user-ewaldn" package. It is only
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enabled if LAMMPS was built with that package. See the "Making
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LAMMPS"_Section_start.html#2_3 section for more info.
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When using a long-range pairwise TIP4P potential, you must use kspace
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style {pppm/tip4p} and vice versa.
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[Related commands:]
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"kspace_modify"_kspace_modify.html, "pair_style
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lj/cut/coul/long"_pair_lj.html, "pair_style
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lj/charmm/coul/long"_pair_charmm.html, "pair_style
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lj/coul"_pair_lj_coul.html, "pair_style buck/coul/long"_pair_buck.html
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[Default:]
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kspace_style none :pre
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:line
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:link(Darden)
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[(Darden)] Darden, York, Pedersen, J Chem Phys, 98, 10089 (1993).
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:link(Hockney)
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[(Hockney)] Hockney and Eastwood, Computer Simulation Using Particles,
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Adam Hilger, NY (1989).
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:link(Pollock)
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[(Pollock)] Pollock and Glosli, Comp Phys Comm, 95, 93 (1996).
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:link(Veld)
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[(Veld)] In 't Veld, Ismail, Grest, J Chem Phys, in press (2007).
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