Syntax:
-fix ID group-ID ave/spatial Nevery Nfreq dim origin delta file keyword value ... +fix ID group-ID ave/spatial Nevery Nfreq dim origin delta file style args keyword value ...-
density arg = mass or number + mass = compute mass density + number = compute number density + atom arg = vx or vy or vz or fx or fy or fz + compute arg = compute-ID that calculates per-atom quantities ++
keyword = norm or units + norm value = all or sample + units value = box or lattice ++
density value = none - atom value = vx or vy or vz or fx or fy or fz - compute value = compute-ID that calculates per-atom quantities -
Examples:
fix 1 all ave/time 10000 10000 z lower 2.0 centro.profile compute myCentro -fix 1 flow ave/time 100 1000 y 0.0 1.0 vel.profile atom vx +fix 1 flow ave/time 100 1000 y 0.0 1.0 vel.profile atom vx norm sample +fix 1 flow ave/time 100 1000 y 0.0 1.0 dens.profile density mass
Description:
@@ -43,20 +62,20 @@ to spatially average per-atom properties such as velocity or energy or a quantity calculated by an equation you define; see the variable atom command. -The density keyword means to simply count the number of atoms in
-each layer. The atom keyword allows an atom property such as
-x-velocity to be specified. The compute keyword allows
-specification of a compute which will be invoked to
-calculate the desired property. The compute can be previously defined
-in the input script. Note that the "compute variable/atom" style
-allows you to calculate any quantity for an atom that can be specified
-by a variable atom equation. Users can also write
-code for their own compute styles and add them to
+ The density styles means to simply count the number of atoms in each
+layer, either by mass or number. The atom style allows an atom
+property such as x-velocity to be specified. The compute style
+allows specification of a compute which will be invoked
+to calculate the desired property. The compute can be previously
+defined in the input script. Note that the "compute variable/atom"
+style allows you to calculate any quantity for an atom that can be
+specified by a variable atom equation. Users can also
+write code for their own compute styles and add them to
LAMMPS. Note that the dump custom
command can also be used to output per-atom quantities calculated by a
compute.
For the compute keyword, the fix ave/spatial style uses the per-atom
+ For the compute style, the fix ave/spatial style uses the per-atom
scalar or vector calculated by the compute. See the fix
ave/time command if you wish to time-average a
global quantity, e.g. via a compute that temperature or pressure.
@@ -75,6 +94,14 @@ the box. On subsequent timesteps every atom is mapped to one of the
layers. Atoms beyond the lowermost/uppermost layer are counted in the
first/last layer.
The units keyword determines the meaning of the distance units used
+for the layer thickness delta and origin if it is a coordinate
+value. A box value selects standard distance units as defined by
+the units command, e.g. Angstroms for units = real or
+metal. A lattice value means the distance units are in lattice
+spacings. The lattice command must have been
+previously used to define the lattice spacing.
+ The Nevery and Nfreq arguments specify how the property calculated
for each layer is time-averaged. The property is calculated once each
Nevery timesteps. It is averaged and output every Nfreq timesteps.
@@ -82,6 +109,18 @@ Nfreq must be a multiple of Nevery. In the 2nd example above, the
property is calculated every 100 steps. After 10 calculations, the
average result is written to the file, once every 1000 steps.
The norm keyword also affects how time-averaging is done. For an
+all setting, a layer quantity is summed over all atoms in all
+Nfreq/Nevery samples, as is the count of atoms in the layer. The
+printed value for the layer is Total-quantity / Total-count.
+In other words it is an average over the entire Nfreq timescale.
+ For a sample setting, the quantity is summed over atoms for only a
+single sample, as is the count, and a "average sample value" is
+computed, i.e. Sample-quantity / Sample-count. The printed value for
+the layer is the average of the M "average sample values", where M =
+Nfreq/Nevery. In other words it is an average of an average.
+ Each time info is written to the file, it is in the following format.
A line with the timestep and number of layers is written. Then one
line per layer is written, containing the layer ID (1-N), the
@@ -95,11 +134,6 @@ single value will be printed for each layer. If the compute keyword
is used with a compute that calculates N quantities per atom, then N
values per line will be written, each of them averaged independently.
Note that for the density keyword, the printed count of atoms in the
-layer is actually what you should use to infer a density. The
-calculated value is always 1.0, since it is normalized by the number
-of atoms in the layer.
- For the compute keyword, the calculation performed by the compute in
on the group defined by the compute. However, only atoms in the fix
group are included in the layer averaging. LAMMPS prints a warning if
@@ -115,6 +149,8 @@ fix ave/spatial, it can slow down a simulation.
Default: none
+ Default:
+ The option defaults are norm = all and units = lattice.