diff --git a/doc/src/pair_lj_cut_tip4p.rst b/doc/src/pair_lj_cut_tip4p.rst index 7198b60159..d95f356ab7 100644 --- a/doc/src/pair_lj_cut_tip4p.rst +++ b/doc/src/pair_lj_cut_tip4p.rst @@ -58,6 +58,40 @@ Examples Description """"""""""" +The *lj/cut/tip4p* styles implement the TIP4P water model of +:ref:`(Jorgensen) ` and similar models, which introduce a +massless site M located a short distance away from the oxygen atom along +the bisector of the HOH angle. The atomic types of the oxygen and +hydrogen atoms, the bond and angle types for OH and HOH interactions, +and the distance to the massless charge site are specified as pair_style +arguments and are used to identify the TIP4P-like molecules and +determine the position of the M site from the positions of the hydrogen +and oxygen atoms of the water molecules. The M site location is used +for all Coulomb interactions instead of the oxygen atom location, also +with all other atom types, while the location of the oxygen atom is used +for the Lennard-Jones interactions. Style *lj/cut/tip4p/cut* uses a +cutoff for Coulomb interactions; style *lj/cut/tip4p/long* is for use +with a long-range Coulombic solver (Ewald or PPPM). + +.. note:: + + For each TIP4P water molecule in your system, the atom IDs for + the O and 2 H atoms must be consecutive, with the O atom first. This + is to enable LAMMPS to "find" the 2 H atoms associated with each O + atom. For example, if the atom ID of an O atom in a TIP4P water + molecule is 500, then its 2 H atoms must have IDs 501 and 502. + +See the :doc:`Howto tip4p ` page for more information +on how to use the TIP4P pair styles and lists of parameters to set. +Note that the neighbor list cutoff for Coulomb interactions is +effectively extended by a distance 2\*qdist when using the TIP4P pair +style, to account for the offset distance of the fictitious charges on +O atoms in water molecules. Thus it is typically best in an +efficiency sense to use a LJ cutoff >= Coulombic cutoff + 2\*qdist, to +shrink the size of the neighbor list. This leads to slightly larger +cost for the long-range calculation, so you can test the trade-off for +your model. + The *lj/cut/tip4p* styles compute the standard 12/6 Lennard-Jones potential, given by @@ -91,34 +125,6 @@ specified for this style means that pairwise interactions within this distance are computed directly; interactions outside that distance are computed in reciprocal space. -The *lj/cut/tip4p* styles implement the TIP4P -water model of :ref:`(Jorgensen) `, which introduces a massless -site located a short distance away from the oxygen atom along the -bisector of the HOH angle. The atomic types of the oxygen and -hydrogen atoms, the bond and angle types for OH and HOH interactions, -and the distance to the massless charge site are specified as -pair_style arguments. Style *lj/cut/tip4p/cut* uses a cutoff for -Coulomb interactions; style *lj/cut/tip4p/long* is for use with a -long-range Coulombic solver (Ewald or PPPM). - -.. note:: - - For each TIP4P water molecule in your system, the atom IDs for - the O and 2 H atoms must be consecutive, with the O atom first. This - is to enable LAMMPS to "find" the 2 H atoms associated with each O - atom. For example, if the atom ID of an O atom in a TIP4P water - molecule is 500, then its 2 H atoms must have IDs 501 and 502. - -See the :doc:`Howto tip4p ` page for more information -on how to use the TIP4P pair styles and lists of parameters to set. -Note that the neighbor list cutoff for Coulomb interactions is -effectively extended by a distance 2\*qdist when using the TIP4P pair -style, to account for the offset distance of the fictitious charges on -O atoms in water molecules. Thus it is typically best in an -efficiency sense to use a LJ cutoff >= Coulombic cutoff + 2\*qdist, to -shrink the size of the neighbor list. This leads to slightly larger -cost for the long-range calculation, so you can test the trade-off for -your model. Coefficients """"""""""""