Undated units conversion factors.

git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@262 f3b2605a-c512-4ea7-a41b-209d697bcdaa

doc/units.html

@@ -30,6 +30,10 @@ and data file, as well as quantities output to the screen, log file,
 and dump files.  Typically, this command is used at the very beginning
 of an input script.
 </P>
+<P>For real and metallic units, 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.
+</P>
 <P>For style <I>lj</I>, all quantities are unitless:
 </P>
 <UL><LI>distance = sigma