132
135
displacement applied to faces of an originally orthogonal box to
133
136
transform it into the parallelepiped.
135
The tilt factors (xy,xz,yz) can not skew the box more than half the
136
distance of the corresponding parallel box length. For example, if
137
xlo = 2 and xhi = 12, then the x box length is 10 and the xy tilt
138
factor must be between -5 and 5. Similarly, both xz and yz must be
139
between -(xhi-xlo)/2 and +(yhi-ylo)/2. Note that this is not a
140
limitation, since if the maximum tilt factor is 5 (as in this
138
By default, the tilt factors (xy,xz,yz) can not skew the box more than
139
half the distance of the corresponding parallel box length. For
140
example, if xlo = 2 and xhi = 12, then the x box length is 10 and the
141
xy tilt factor must be between -5 and 5. Similarly, both xz and yz
142
must be between -(xhi-xlo)/2 and +(yhi-ylo)/2. Note that this is not
143
a limitation, since if the maximum tilt factor is 5 (as in this
141
144
example), then configurations with tilt = ..., -15, -5, 5, 15, 25,
142
... are all geometrically equivalent.
145
... are all geometrically equivalent. If you wish to define a box
146
with tilt factors that exceed these limits, you can use the "box
147
tilt"_box.html command, with a setting of {large}; a setting of
148
{small} is the default.
144
150
See "Section_howto 12"_Section_howto.html#howto_12 of the doc pages
145
151
for a geometric description of triclinic boxes, as defined by LAMMPS,
146
152
and how to transform these parameters to and from other commonly used
147
153
triclinic representations.
149
When a triclinic system is used, the simulation domain must be
150
periodic in any dimensions with a non-zero tilt factor, as defined by
151
the "boundary"_boundary.html command. I.e. if the xy tilt factor is
152
non-zero, then both the x and y dimensions must be periodic.
153
Similarly, x and z must be periodic if xz is non-zero and y and z must
154
be periodic if yz is non-zero. Also note that if your simulation will
155
tilt the box, e.g. via the "fix deform"_fix_deform.html command, the
156
simulation box must be defined as triclinic, even if the tilt factors
155
When a triclinic system is used, the simulation domain should normally
156
be periodic in the dimension that the tilt is applied to, which is
157
given by the second dimension of the tilt factor (e.g. y for xy tilt).
158
This is so that pairs of atoms interacting across that boundary will
159
have one of them shifted by the tilt factor. Periodicity is set by
160
the "boundary"_boundary.html command. For example, if the xy tilt
161
factor is non-zero, then the y dimension should be periodic.
162
Similarly, the z dimension should be periodic if xz or yz is non-zero.
163
LAMMPS does not require this periodicity, but you may lose atoms if
164
this is not the case.
166
Also note that if your simulation will tilt the box, e.g. via the "fix
167
deform"_fix_deform.html command, the simulation box must be setup to
168
be triclinic, even if the tilt factors are initially 0.0. You can
169
also change an orthogonal box to a triclinic box or vice versa by
170
using the "change box"_change_box.html command with its {ortho} and
159
173
For 2d simulations, the {zlo zhi} values should be set to bound the z
160
174
coords for atoms that appear in the file; the default of -0.5 0.5 is
180
194
"fixed" boundary conditions (see the "boundary"_boundary.html
181
195
command). When using "shrink-wrap" boundary conditions (see the
182
196
"boundary"_boundary.html command), a huge (mostly empty) box may cause
183
a parallel simulation to lose atoms the first time that LAMMPS
184
shrink-wraps the box around the atoms.
197
a parallel simulation to lose atoms when LAMMPS shrink-wraps the box
198
around the atoms. The read_data command will generate an error
186
201
The "extra bond per atom" setting (angle, dihedral, improper) is only
187
202
needed if new bonds (angles, dihedrals, impropers) will be added to
190
205
space in LAMMPS data structures for storing the new bonds (angles,
191
206
dihedrals, impropers).
193
The "extra special per atom" setting is only needed if new molecules
208
The "extra special per atom" setting is typically only needed if new
209
bonds/angles/etc will be added to the system, e.g. by using the "fix
210
bond/create"_fix_bond_create.html command. Or if entire new molecules
194
211
will be added to the system, e.g. by using the "fix
195
212
deposit"_fix_deposit.html or "fix pour"_fix_pour.html commands, which
196
213
will have more special 1-2,1-3,1-4 neighbors than any other molecules
197
defined in the data file. This will pre-allocate space in the LAMMPS
198
data structures for storing these neighbors. See the
214
defined in the data file. Using this setting will pre-allocate space
215
in the LAMMPS data structures for storing these neighbors. See the
199
216
"special_bonds"_special_bonds.html and "molecule"_molecule.html doc
200
217
pages for more discussion of 1-2,1-3,1-4 neighbors.