The group specified with this command is ignored. However, note that specified values may represent calculations performed by computes and @@ -337,7 +340,8 @@ minimization.
Related commands:
-compute, fix ave/time, fix
+ fix ave/correlate/long,
+compute, fix ave/time, fix
ave/atom, fix ave/spatial,
fix ave/histo, variable
Syntax:
+ Examples:
+ Description:
+ This fix is similar in spirit and syntax to the fix
+ave/correlate. However, this fix allows the
+efficient calculation of time correlation functions on the fly over
+extremely long time windows without too much CPU overhead, using a
+multiple-tau method (Ramirez) that decreases the resolution
+of the stored correlation function with time.
+ The group specified with this command is ignored. However, note that
+specified values may represent calculations performed by computes and
+fixes which store their own "group" definitions.
+ Each listed value can be the result of a compute or fix or the
+evaluation of an equal-style variable. See the fix
+ave/correlate doc page for details.
+ The Nevery and Nfreq arguments specify on what timesteps the input
+values will be used to calculate correlation data, and the frequency
+with which the time correlation functions will be output to a file.
+Note that there is no Nrepeat argument, unlike the fix
+ave/correlate command.
+ The optional keywords ncorr, nlen, and ncount are unique to this
+command and determine the number of correlation points calculated and
+the memory and CPU overhead used by this calculation. Nlen and
+ncount determine the amount of averaging done at longer correlation
+times. The default values nlen=16, ncount=2 ensure that the
+systematic error of the multiple-tau correlator is always below the
+level of the statistical error of a typical simulation (which depends
+on the ensemble size and the simulation length).
+ The maximum correlation time (in time steps) that can be reached is
+given by the formula (nlen-1) * ncount^(ncorr-1). Longer correlation
+times are discarded and not calculated. With the default values of
+the parameters (ncorr=20, nlen=16 and ncount=2), this corresponds to
+7864320 time steps. If longer correlation times are needed, the value
+of ncorr should be increased. Using nlen=16 and ncount=2, with
+ncorr=30, the maximum number of steps that can be correlated is
+80530636808. If ncorr=40, correlation times in excess of 8e12 time
+steps can be calculated.
+ The total memory needed for each correlation pair is roughly
+4*ncorr*nlen*8 bytes. With the default values of the parameters, this
+corresponds to about 10 KB.
+ For the meaning of the additional optional keywords, see the fix
+ave/correlate doc page.
+ Restart, fix_modify, output, run start/stop, minimize info:
+ Since this fix in intended for the calculation of time correlation
+functions over very long MD simulations, the information about this
+fix is written automatically to binary restart files, so that the time
+correlation calculation can continue in subsequent simulations. None
+of the fix_modify options are relevant to this fix.
+ No parameter of this fix can be used with the start/stop keywords of
+the run command. This fix is not invoked during energy minimization.
+ Restrictions:
+ This compute is part of the USER-MISC package. It is only enabled if
+LAMMPS was built with that package. See the Making
+LAMMPS section for more info.
+ Related commands:
+ Default: none
+ The option defaults for keywords that are also keywords for the fix
+ave/correlate command are as follows: type =
+auto, start = 0, no file output, title 1,2 = strings as described on
+the fix ave/correlate doc page.
+ The option defaults for keywords unique to this command are as
+follows: ncorr=20, nlen=16, ncount=2.
+
+
+fix ave/correlate/long command
+
+fix ID group-ID ave/correlate/long Nevery Nfreq value1 value2 ... keyword args ...
+
+
+ c_ID = global scalar calculated by a compute with ID
+ c_ID[I] = Ith component of global vector calculated by a compute with ID
+ f_ID = global scalar calculated by a fix with ID
+ f_ID[I] = Ith component of global vector calculated by a fix with ID
+ v_name = global value calculated by an equal-style variable with name
+
+ type arg = auto or upper or lower or auto/upper or auto/lower or full
+ auto = correlate each value with itself
+ upper = correlate each value with each succeeding value
+ lower = correlate each value with each preceding value
+ auto/upper = auto + upper
+ auto/lower = auto + lower
+ full = correlate each value with every other value, including itself = auto + upper + lower
+ start args = Nstart
+ Nstart = start accumulating correlations on this timestep
+ file arg = filename
+ filename = name of file to output correlation data to
+ overwrite arg = none = overwrite output file with only latest output
+ title1 arg = string
+ string = text to print as 1st line of output file
+ title2 arg = string
+ string = text to print as 2nd line of output file
+ ncorr arg = Ncorrelators
+ Ncorrelators = number of correlators to store
+ nlen args = Nlen
+ Nlen = length of each correlator
+ ncount args = Ncount
+ Ncount = number of values over which succesive correlators are averaged
+
+
+fix 1 all ave/correlate/long 5 1000 c_myTemp file temp.correlate
+fix 1 all ave/correlate/long 1 10000 &
+ c_thermo_press[1] c_thermo_press[2] c_thermo_press[3] &
+ type upper title1 "My correlation data" nlen 15 ncount 3
+
+
+
+
+
+
(Ramirez) J. Ramirez, S.K. Sukumaran, B. Vorselaars and +A.E. Likhtman, J. Chem. Phys. 133, 154103 (2010). +
+