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55 lines
1.6 KiB
Plaintext
55 lines
1.6 KiB
Plaintext
"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
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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,Commands_all.html)
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:line
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SPC water model :h3
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The SPC water model specifies a 3-site rigid water molecule with
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charges and Lennard-Jones parameters assigned to each of the 3 atoms.
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In LAMMPS the "fix shake"_fix_shake.html command can be used to hold
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the two O-H bonds and the H-O-H angle rigid. A bond style of
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{harmonic} and an angle style of {harmonic} or {charmm} should also be
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used.
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These are the additional parameters (in real units) to set for O and H
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atoms and the water molecule to run a rigid SPC model.
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O mass = 15.9994
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H mass = 1.008
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O charge = -0.820
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H charge = 0.410
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LJ epsilon of OO = 0.1553
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LJ sigma of OO = 3.166
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LJ epsilon, sigma of OH, HH = 0.0
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r0 of OH bond = 1.0
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theta of HOH angle = 109.47 :all(b),p
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Note that as originally proposed, the SPC model was run with a 9
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Angstrom cutoff for both LJ and Coulombic terms. It can also be used
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with long-range Coulombics (Ewald or PPPM in LAMMPS), without changing
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any of the parameters above, though it becomes a different model in
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that mode of usage.
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The SPC/E (extended) water model is the same, except
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the partial charge assignments change:
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O charge = -0.8476
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H charge = 0.4238 :all(b),p
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See the "(Berendsen)"_#howto-Berendsen reference for more details on both
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the SPC and SPC/E models.
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Wikipedia also has a nice article on "water
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models"_http://en.wikipedia.org/wiki/Water_model.
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:line
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:link(howto-Berendsen)
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[(Berendsen)] Berendsen, Grigera, Straatsma, J Phys Chem, 91,
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6269-6271 (1987).
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