docs kcal definition, real units

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1

Hi Lammps-users,

I think there might be an error in the docs. The units doc
page says, "For the definition of Kcal in real units, LAMMPS
uses the thermochemical calorie = 4.184 J."

It seems that the definition in lammps is 1 KCal = 4184 J for
real units.

You can test it with a minimization using LJ/Cut comparing real
and metal units (see attached). The pressure of the minimized
geometry is the same only when 1 KCal = 4184 J. This conversion
also shows up in the argon heat/flux example.

Best,
John

metal.in (726 Bytes)

metal.out (2.45 KB)

real.in (523 Bytes)

real.out (1.87 KB)

wrong.in (760 Bytes)

wrong.out (2.54 KB)

2

Hi Lammps-users,

I think there might be an error in the docs. The units doc
page says, "For the definition of Kcal in real units, LAMMPS
uses the thermochemical calorie = 4.184 J."

It seems that the definition in lammps is 1 KCal = 4184 J for
real units.

1 cal = 4.184 J
1 kcal = 1000 cal = 1000 * 4.184 J = 4184 J

please explain where the problem is.

thanks,
    axel.