forked from lijiext/lammps
101 lines
3.2 KiB
Plaintext
101 lines
3.2 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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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} :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 :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. When such a solver is used in
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conjunction with an appropriate pair style, the cutoff for Coulombic
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interactions is effectively infinite; each charge in the system
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interacts with charges in an infinite array of periodic images of the
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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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When a kspace style is used, a pair style that includes the
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short-range correction to the pairwise Coulombic forces must also be
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selected. These styles are ones that have a {coul/long} in their
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style name.
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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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[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_2 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"_pair_style.html
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lj/cut/coul/long, "pair_style"_pair_style.html lj/charmm/coul/long
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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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