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clarified the README

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Steve Plimpton 2019-10-08 18:14:32 -06:00
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examples/UNITS/README
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@ -33,15 +33,20 @@ unscaled back to LJ units. So that you can see the outputs are the
same if you examine the log files. Comments about this comparison
are at the bottom of the real and metal scripts.
If you understand LJ reduced units (see Allen & Tildesley's Computer
Simulation of Liquids, Appendix B for a nice discussion), and you
study these scripts, you should be able to convert an input script in
one set of units to an identical input script in an alternate set of
units. Where "identical" means it runs the same simulation in a
statistical sense. For example you could easily define conversion
factors from real to metal units or vice versa, and use them to scale
inputs and outputs in one script to produce a script in alternate
units.
These 3 scripts are provided, because converting from lj reduced units
to physical units (e.g. real or metal) or vice versa is the trickiest
case. Converting input scripts between 2 sets of physical units
(e.g. reak <--> metal) is much easier. But you can use the same ideas
as in these scripts; just define a set of scale/unscale factors.
See Allen & Tildesley's Computer Simulation of Liquids, Appendix B for
a nice discussion of reduced units. It will explain the conversion
formulas used in the real and metal scripts.
Hopefully, if you study these scripts, you should be able to convert
an input script of your own, written in one set of units, to an
identical input script in an alternate set of units. Where
"identical" means it runs the same simulation in a statistical sense.
You can find the full set of scale factors LAMMPS uses internally for
different unit systems it supports, at the top of the src/udpate.cpp