From 8d72e673ffdaf92bedb70328fcbadb70eac28f72 Mon Sep 17 00:00:00 2001 From: sjplimp Date: Fri, 26 Jun 2015 17:33:25 +0000 Subject: [PATCH] git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@13494 f3b2605a-c512-4ea7-a41b-209d697bcdaa --- doc/units.html | 18 ++++++++++++++++++ doc/units.txt | 18 ++++++++++++++++++ 2 files changed, 36 insertions(+) diff --git a/doc/units.html b/doc/units.html index 5e2f07de4c..d532b2ae32 100644 --- a/doc/units.html +++ b/doc/units.html @@ -34,6 +34,24 @@ of an input script. www.physics.nist.gov. For the definition of Kcal in real units, LAMMPS uses the thermochemical calorie = 4.184 J.

+

The choice you make for units simply sets some internal conversion +factors within LAMMPS. This means that any simulation you perform for +one choice of units can be duplicated with any other unit setting +LAMMPS supports. In this context "duplicate" means the particles will +have identical trajectories and all output generated by the simulation +will be identical. This will be the case for some number of timesteps +until round-off effects accumulate, since the conversion factors for +two different unit systems are not identical to infinite precision. +

+

To perform the same simulation in a different set of units you must +change all the unit-based input parameters in your input script and +other input files (data file, potential files, etc) correctly to the +new units. And you must correctly convert all output from the new +units to the old units when comparing to the original results. That +is often not simple to do. +

+
+

For style lj, all quantities are unitless. Without loss of generality, LAMMPS sets the fundamental quantities mass, sigma, epsilon, and the Boltzmann constant = 1. The masses, distances, diff --git a/doc/units.txt b/doc/units.txt index 0806095237..1cdeb1bd15 100644 --- a/doc/units.txt +++ b/doc/units.txt @@ -31,6 +31,24 @@ For all units except {lj}, LAMMPS uses physical constants from www.physics.nist.gov. For the definition of Kcal in real units, LAMMPS uses the thermochemical calorie = 4.184 J. +The choice you make for units simply sets some internal conversion +factors within LAMMPS. This means that any simulation you perform for +one choice of units can be duplicated with any other unit setting +LAMMPS supports. In this context "duplicate" means the particles will +have identical trajectories and all output generated by the simulation +will be identical. This will be the case for some number of timesteps +until round-off effects accumulate, since the conversion factors for +two different unit systems are not identical to infinite precision. + +To perform the same simulation in a different set of units you must +change all the unit-based input parameters in your input script and +other input files (data file, potential files, etc) correctly to the +new units. And you must correctly convert all output from the new +units to the old units when comparing to the original results. That +is often not simple to do. + +:line + For style {lj}, all quantities are unitless. Without loss of generality, LAMMPS sets the fundamental quantities mass, sigma, epsilon, and the Boltzmann constant = 1. The masses, distances,