forked from lijiext/lammps
504 lines
15 KiB
Plaintext
504 lines
15 KiB
Plaintext
"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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read_data command :h3
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[Syntax:]
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read_data file :pre
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file = name of data file to read in :ul
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[Examples:]
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read_data data.lj
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read_data ../run7/data.polymer.gz :pre
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[Description:]
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Read in a data file containing information LAMMPS needs to run a
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simulation. The file can be ASCII text or a gzipped text file
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(detected by a .gz suffix). This is one of 3 ways to specify initial
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atom coordinates; see the "read_restart"_read_restart.html and
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"create_atoms"_create_atoms.html commands for alternative methods.
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The structure of the data file is important, though many settings and
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sections are optional or can come in any order. See the examples
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directory for sample data files for different problems.
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A data file has a header and a body. The header appears first. The
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first line of the header is always skipped; it typically contains a
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description of the file. Then lines are read one at a time. Lines
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can have a trailing comment starting with '#' that is ignored. If the
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line is blank (only whitespace after comment is deleted), it is
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skipped. If the line contains a header keyword, the corresponding
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value(s) is read from the line. If it doesn't contain a header
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keyword, the line begins the body of the file.
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The body of the file contains zero or more sections. The first line
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of a section has only a keyword. The next line is skipped. The
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remaining lines of the section contain values. The number of lines
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depends on the section keyword as described below. Zero or more blank
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lines can be used between sections. Sections can appear in any order,
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with a few exceptions as noted below.
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The formatting of individual lines in the data file (indentation,
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spacing between words and numbers) is not important except that header
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and section keywords (e.g. atoms, xlo xhi, Masses, Bond Coeffs) must
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be capitalized as shown and can't have extra white space between their
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words - e.g. two spaces or a tab between "Bond" and "Coeffs" is not
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valid.
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:line
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These are the recognized header keywords. Header lines can come in
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any order. The value(s) is read from the beginning of the line. Thus
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the keyword {atoms} should be in a line like "1000 atoms" and the
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keyword {ylo yhi} should be in a line like "-10.0 10.0 ylo yhi". All
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these settings have a default value of 0, except the lo/hi box size
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defaults are -0.5 and 0.5. A line need only appear if the value is
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different than the default.
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{atoms} = # of atoms in system
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{bonds} = # of bonds in system
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{angles} = # of angles in system
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{dihedrals} = # of dihedrals in system
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{impropers} = # of impropers in system
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{atom types} = # of atom types in system
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{bond types} = # of bond types in system
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{angle types} = # of angle types in system
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{dihedral types} = # of dihedral types in system
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{improper types} = # of improper types in system
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{xlo xhi} = simulation box boundaries in x dimension
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{ylo yhi} = simulation box boundaries in y dimension
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{zlo zhi} = simulation box boundaries in z dimension :ul
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For 2d simulations, the {zlo zhi} values should be set to bound the z
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coords for atoms that appear in the file; the default of -0.5 0.5 is
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valid if all z coords are 0.0.
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The initial simulation box size is determined by the lo/hi settings.
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In any dimension, the system may be periodic or non-periodic; see the
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"boundary"_boundary.html command.
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If the system is non-periodic (in a dimension), then all atoms in the
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data file should have coordinates (in that dimension) between the lo
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and hi values. Furthermore, if running in parallel, the lo/hi values
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should be just a bit smaller/larger than the min/max extent of atoms.
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For example, if your atoms extend from 0 to 50, you should not specify
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the box bounds as -10000 and 10000. Since LAMMPS uses the specified
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box size to layout the 3d grid of processors, this will be sub-optimal
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and may cause a parallel simulation to lose atoms when LAMMPS
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shrink-wraps the box to the atoms.
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If the system is periodic (in a dimension), then atom coordinates can
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be outside the bounds; they will be remapped (in a periodic sense)
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back inside the box.
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:line
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These are the section keywords for the body of the file.
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{Atoms, Velocities, Masses, Dipoles} = atom-property sections
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{Bonds, Angles, Dihedrals, Impropers} = molecular topolgy sections
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{Pair Coeffs, Bond Coeffs, Angle Coeffs, Dihedral Coeffs, \
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Improper Coeffs} = force field sections
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{BondBond Coeffs, BondAngle Coeffs, MiddleBondTorsion Coeffs, \
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EndBondTorsion Coeffs, AngleTorsion Coeffs, AngleAngleTorsion Coeffs, \
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BondBond13 Coeffs, AngleAngle Coeffs} = class 2 force field sections :ul
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Each section is now listed in alphabetic order. The format of each
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section is described including the number of lines it must contain and
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rules (if any) for where it can appear in the data file.
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Any individual line in the various sections can have a trailing
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comment starting with "#" for annotation purposes. E.g. in the
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Atoms section:
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10 1 17 -1.0 10.0 5.0 6.0 # salt ion :pre
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:line
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{Angle Coeffs} section:
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one line per angle type :ulb,l
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line syntax: ID coeffs :l
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ID = angle type (1-N)
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coeffs = list of coeffs :pre
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example: :l
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6 70 108.5 0 0 :pre
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:ule
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The number and meaning of the coefficients are specific to the defined
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angle style. See the "angle_style"_angle_style.html and
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"angle_coeff"_angle_coeff.html commands for details. Coefficients can
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also be set via the "angle_coeff"_angle_coeff.html command in the
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input script.
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:line
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{AngleAngle Coeffs} section:
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one line per improper type :ulb,l
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line syntax: ID coeffs :l
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ID = improper type (1-N)
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coeffs = list of coeffs (see "improper_coeff"_improper_coeff.html) :pre
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:ule
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:line
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{AngleAngleTorsion Coeffs} section:
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one line per dihedral type :ulb,l
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line syntax: ID coeffs :l
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ID = dihedral type (1-N)
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coeffs = list of coeffs (see "dihedral_coeff"_dihedral_coeff.html) :pre
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:ule
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:line
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{Angles} section:
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one line per angle :ulb,l
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line syntax: ID type atom1 atom2 atom3 :l
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ID = number of angle (1-Nangles)
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type = angle type (1-Nangletype)
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atom1,atom2,atom3 = IDs of 1st,2nd,3rd atoms in angle :pre
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example: :b
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2 2 17 29 430 :pre
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:ule
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The 3 atoms are ordered linearly within the angle. Thus the central
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atom (around which the angle is computed) is the atom2 in the list.
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E.g. H,O,H for a water molecule. The {Angles} section must appear
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after the {Atoms} section. All values in this section must be
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integers (1, not 1.0).
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:line
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{AngleTorsion Coeffs} section:
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one line per dihedral type :ulb,l
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line syntax: ID coeffs :l
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ID = dihedral type (1-N)
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coeffs = list of coeffs (see "dihedral_coeff"_dihedral_coeff.html) :pre
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:ule
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:line
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{Atoms} section:
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one line per atom
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line syntax: depends on atom style :ul
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This is the list of all possible quantities that can appear on each
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line of this section:
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atom-ID = integer ID of atom
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molecule-ID = integer ID of molecule the atom belongs to
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type-ID = integer type ID of atom (1-Ntype)
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q = charge on atom
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diameter = diameter of atom
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density = density of atom
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x,y,z = coordinates of atom
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mux,muy,muz = components of dipole orientation of atom
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nx,ny,nz = image indices for atom :ul
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Which of these quantities are actually listed depends on the "atom
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style"_atom_style.html. This is the list of which styles require each
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quantity:
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atom-ID = all styles
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molecule-ID = angle, bond, molecular, full styles
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type-ID = all styles
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q = charge, dipole, full styles
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diameter = granular style
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density = granular style
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x,y,z = all styles
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mux,muy,muz = dipole style
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nx,ny,nz = optional for all styles (see below) :ul
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Any quantity that is used by the atom style appears in the order
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listed above. Thus if the atom style is {atomic}, an atom line should
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have 5 quantities: atom-ID, type-ID, x, y, z. If the atom style is
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{hybrid eam dipole molecular}, then an atom line should have 10
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quantites: atom-ID, molecule-ID, type-ID, q, x, y, z, mux, muy, muz.
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The units for these quantities depend on the unit style; see the
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"units"_units.html command for details.
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For 2d simulations specify z as 0.0, or whatever value is within the
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{zlo zhi} setting in the data file header.
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The atom-ID is used to identify the atom throughout the simulation and
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in dump files. Normally, it is a unique value from 1 to Natoms for
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each atom. Unique values larger than Natoms can be used, but they
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will cause extra memory to be allocated on each processor, if an atom
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map array is used (see the "atom_modify"_atom_modify.html command).
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If an atom map array is not used (e.g. an atomic system with no
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bonds), velocities are not assigned in the data file, and you don't
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care if unique atom IDs appear in dump files, then IDs can be set to
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non-unique values > 0.
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The molecule ID is a 2nd identifier attached to an atom. Normally, it
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is a number from 1 to N, identifying which molecule the atom belongs
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to. It can be 0 if it is an unbonded atom or if you don't care about
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molecule assignments.
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An {Atoms} section must appear in the data file if natoms > 0 in the
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header section. The atoms can be listed in any order.
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Atom lines (all or none of them) can optionally list 3 final integer
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values: nx,ny,nz. For periodic dimensions, they specify which image
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of the box the atom is considered to be in. An image of 0 means the
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box as defined. A value of 2 means add 2 box lengths to get the true
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value. A value of -1 means subtract 1 box length to get the true
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value. LAMMPS updates these flags as atoms cross periodic boundaries
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during the simulation. The flags can be output via the
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"dump"_dump.html and "dump_modify"_dump_modify.html commands. If
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nx,ny,nz values are not set in the data file, LAMMPS initializes them
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to 0.
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Atom velocities are set to 0.0 when the {Atoms} section is read. They
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may later be set by a {Velocities} section or by a
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"velocity"_velocity.html command in the input script.
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:line
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{Bond Coeffs} section:
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one line per bond type :ulb,l
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line syntax: ID coeffs :l
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ID = bond type (1-N)
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coeffs = list of coeffs :pre
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example: :l
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4 250 1.49 :pre
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:ule
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The number and meaning of the coefficients are specific to the defined
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bond style. See the "bond_style"_bond_style.html and
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"bond_coeff"_bond_coeff.html commands for details. Coefficients can
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also be set via the "bond_coeff"_bond_coeff.html command in the input
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script.
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:line
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{BondAngle Coeffs} section:
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one line per angle type :ulb,l
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line syntax: ID coeffs :l
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ID = angle type (1-N)
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coeffs = list of coeffs (see class 2 section of "angle_coeff"_angle_coeff.html) :pre
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:ule
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:line
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{BondBond Coeffs} section:
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one line per angle type :ulb,l
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line syntax: ID coeffs :l
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ID = angle type (1-N)
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coeffs = list of coeffs (see class 2 section of "angle_coeff"_angle_coeff.html) :pre
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:ule
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:line
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{BondBond13 Coeffs} section:
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one line per dihedral type :ulb,l
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line syntax: ID coeffs :l
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ID = dihedral type (1-N)
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coeffs = list of coeffs (see class 2 section of "dihedral_coeff"_dihedral_coeff.html) :pre
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:ule
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:line
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{Bonds} section:
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one line per bond :ulb,l
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line syntax: ID type atom1 atom2 :l
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ID = bond number (1-Nbonds)
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type = bond type (1-Nbondtype)
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atom1,atom2 = IDs of 1st,2nd atoms in bond :pre
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example: :l
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12 3 17 29 :pre
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:ule
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The {Bonds} section must appear after the {Atoms} section. All values
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in this section must be integers (1, not 1.0).
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:line
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{Dihedral Coeffs} section:
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one line per dihedral type :ulb,l
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line syntax: ID coeffs :l
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ID = dihedral type (1-N)
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coeffs = list of coeffs :pre
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example: :l
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3 0.6 1 0 1 :pre
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:ule
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The number and meaning of the coefficients are specific to the defined
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dihedral style. See the "dihedral_style"_dihedral_style.html and
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"dihedral_coeff"_dihedral_coeff.html commands for details.
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Coefficients can also be set via the
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"dihedral_coeff"_dihedral_coeff.html command in the input script.
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:line
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{Dihedrals} section:
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one line per dihedral :ulb,l
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line syntax: ID type atom1 atom2 atom3 atom4 :l
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ID = number of dihedral (1-Ndihedrals)
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type = dihedral type (1-Ndihedraltype)
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atom1,atom2,atom3,atom4 = IDs of 1st,2nd,3rd,4th atoms in dihedral :pre
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example: :l
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12 4 17 29 30 21 :pre
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:ule
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The 4 atoms are ordered linearly within the dihedral. The {Dihedrals}
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section must appear after the {Atoms} section. All values in this
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section must be integers (1, not 1.0).
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:line
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{Dipoles} section:
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one line per atom type :ulb,l
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line syntax: ID dipole-moment :
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ID = atom type (1-N)
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dipole-moment = value of dipole moment :pre
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example: :l
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2 0.5 :pre
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:ule
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This defines the dipole moment of each atom type (which can be 0.0 for
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some types). This can also be set via the "dipole"_dipole.html
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command in the input script.
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:line
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{EndBondTorsion Coeffs} section:
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one line per dihedral type :ulb,l
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line syntax: ID coeffs :l
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ID = dihedral type (1-N)
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coeffs = list of coeffs (see class 2 section of "dihedral_coeff"_dihedral_coeff.html) :pre
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:ule
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:line
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{Improper Coeffs} section:
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one line per improper type :ulb,l
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line syntax: ID coeffs :l
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ID = improper type (1-N)
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coeffs = list of coeffs :pre
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example: :l
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2 20 0.0548311 :pre
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:ule
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The number and meaning of the coefficients are specific to the defined
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improper style. See the "improper_style"_improper_style.html and
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"improper_coeff"_improper_coeff.html commands for details.
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Coefficients can also be set via the
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"improper_coeff"_improper_coeff.html command in the input script.
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:line
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{Impropers} section:
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one line per improper :ulb,l
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line syntax: ID type atom1 atom2 atom3 atom4 :l
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ID = number of improper (1-Nimpropers)
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type = improper type (1-Nimpropertype)
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atom1,atom2,atom3,atom4 = IDs of 1st,2nd,3rd,4th atoms in improper :pre
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example: :l
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12 3 17 29 13 100 :pre
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:ule
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The {Impropers} section must appear after the {Atoms} section. All
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values in this section must be integers (1, not 1.0).
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:line
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{Masses} section:
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one line per atom type :ulb,l
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line syntax: ID mass :l
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ID = atom type (1-N)
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mass = mass value :pre
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example: :l
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3 1.01 :pre
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:ule
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This defines the mass of each atom type. This can also be set via the
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"mass"_mass.html command in the input script. This section should not
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be used for atom styles that define a mass for individual atoms -
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e.g. atom style granular.
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:line
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{MiddleBondTorsion Coeffs} section:
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one line per dihedral type :ulb,l
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line syntax: ID coeffs :l
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ID = dihedral type (1-N)
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coeffs = list of coeffs (see class 2 section of "dihedral_coeff"_dihedral_coeff.html) :pre
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:ule
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:line
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{Pair Coeffs} section:
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one line per atom type :ulb,l
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line syntax: ID coeffs :l
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ID = atom type (1-N)
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coeffs = list of coeffs :pre
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example: :l
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3 0.022 2.35197 0.022 2.35197 :pre
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:ule
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The number and meaning of the coefficients are specific to the defined
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pair style. See the "pair_style"_pair_style.html and
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"pair_coeff"_pair_coeff.html commands for details. Coefficients can
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also be set via the "pair_coeff"_pair_coeff.html command in the input
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script.
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:line
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{Velocities} section:
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one line per atom :ulb
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line syntax: atom-ID vx vy vz :l
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atom-ID = integer ID of atom to assign velocity to
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vx,vy,vz = components of velocity of the atom :pre
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example: :l
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45 -3.4 0.05 1.25 :pre
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:ule
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The velocity lines can appear in any order. This section can only be
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used after an {Atoms} section. The {Atoms} section must have assigned
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a unique atom ID to each atom so that velocities can be assigned in
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this way. Velocities can also be set by the "velocity"_velocity.html
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command in the input script.
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:line
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[Restrictions:]
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To read gzipped data files, you must compile LAMMPS with the -DGZIP
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option - see the "Making LAMMPS"_Section_start.html#2_2 section of the
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documentation.
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[Related commands:]
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"read_restart"_read_restart.html, "create_atoms"_create_atoms.html
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[Default:] none
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