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doc/src/Howto_tip4p.rst

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+TIP4P water model
+=================
+
+The four-point TIP4P rigid water model extends the traditional
+three-point TIP3P model by adding an additional site, usually
+massless, where the charge associated with the oxygen atom is placed.
+This site M is located at a fixed distance away from the oxygen along
+the bisector of the HOH bond angle.  A bond style of *harmonic* and an
+angle style of *harmonic* or *charmm* should also be used.
+
+A TIP4P model is run with LAMMPS using either this command
+for a cutoff model:
+
+:doc:`pair\_style lj/cut/tip4p/cut <pair_lj>`
+
+or these two commands for a long-range model:
+
+* :doc:`pair\_style lj/cut/tip4p/long <pair_lj>`
+* :doc:`kspace\_style pppm/tip4p <kspace_style>`
+
+For both models, the bond lengths and bond angles should be held fixed
+using the :doc:`fix shake <fix_shake>` command.
+
+These are the additional parameters (in real units) to set for O and H
+atoms and the water molecule to run a rigid TIP4P model with a cutoff
+:ref:`(Jorgensen) <Jorgensen5>`.  Note that the OM distance is specified in
+the :doc:`pair\_style <pair_style>` command, not as part of the pair
+coefficients.
+
+| O mass = 15.9994
+| H mass = 1.008
+| O charge = -1.040
+| H charge = 0.520
+| r0 of OH bond = 0.9572
+| theta of HOH angle = 104.52
+| OM distance = 0.15
+| LJ epsilon of O-O = 0.1550
+| LJ sigma of O-O = 3.1536
+| LJ epsilon, sigma of OH, HH = 0.0
+| Coulombic cutoff = 8.5
+| 
+
+For the TIP4/Ice model (J Chem Phys, 122, 234511 (2005);
+http://dx.doi.org/10.1063/1.1931662) these values can be used:
+
+| O mass = 15.9994
+| H mass =  1.008
+| O charge = -1.1794
+| H charge =  0.5897
+| r0 of OH bond = 0.9572
+| theta of HOH angle = 104.52
+| OM distance = 0.1577
+| LJ epsilon of O-O = 0.21084
+| LJ sigma of O-O = 3.1668
+| LJ epsilon, sigma of OH, HH = 0.0
+| Coulombic cutoff = 8.5
+| 
+
+For the TIP4P/2005 model (J Chem Phys, 123, 234505 (2005);
+http://dx.doi.org/10.1063/1.2121687), these values can be used:
+
+| O mass = 15.9994
+| H mass =  1.008
+| O charge = -1.1128
+| H charge = 0.5564
+| r0 of OH bond = 0.9572
+| theta of HOH angle = 104.52
+| OM distance = 0.1546
+| LJ epsilon of O-O = 0.1852
+| LJ sigma of O-O = 3.1589
+| LJ epsilon, sigma of OH, HH = 0.0
+| Coulombic cutoff = 8.5
+| 
+
+These are the parameters to use for TIP4P with a long-range Coulombic
+solver (e.g. Ewald or PPPM in LAMMPS):
+
+| O mass = 15.9994
+| H mass = 1.008
+| O charge = -1.0484
+| H charge = 0.5242
+| r0 of OH bond = 0.9572
+| theta of HOH angle = 104.52
+| OM distance = 0.1250
+| LJ epsilon of O-O = 0.16275
+| LJ sigma of O-O = 3.16435
+| LJ epsilon, sigma of OH, HH = 0.0
+| 
+
+Note that the when using the TIP4P pair style, the neighbor list
+cutoff for Coulomb interactions is effectively extended by a distance
+2 \* (OM distance), 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 >= Coulomb
+cutoff + 2\*(OM distance), 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 OM distance and the LJ
+and Coulombic cutoffs are set in the :doc:`pair\_style lj/cut/tip4p/long <pair_lj>` command.
+
+Wikipedia also has a nice article on `water models <http://en.wikipedia.org/wiki/Water_model>`_.
+
+
+----------
+
+
+.. _Jorgensen5:
+
+
+
+**(Jorgensen)** Jorgensen, Chandrasekhar, Madura, Impey, Klein, J Chem
+Phys, 79, 926 (1983).
+
+
+.. _lws: http://lammps.sandia.gov
+.. _ld: Manual.html
+.. _lc: Commands_all.html