From c157f83057bb274e378ed58e00b050d88c5b0063 Mon Sep 17 00:00:00 2001 From: Oliver Beckstein Date: Wed, 2 Sep 2026 18:25:35 -0700 Subject: [PATCH 1/2] update mass unit to CODATA 2010 value - fix #442 - list the implicit mass unit in the units table - add paragraph mentioning CODATA 2010 values and explaining the excess precision in the table (we should have really rounded to significant figures...) --- doc/source/units.rst | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/doc/source/units.rst b/doc/source/units.rst index 16ca8ffbe..00434f209 100644 --- a/doc/source/units.rst +++ b/doc/source/units.rst @@ -28,10 +28,20 @@ Other base units are listed in the table :ref:`table-baseunits`. charge :math:`e` :math:`1.602176565 \times 10^{-19}` As force kJ/(mol·Å) :math:`1.66053892103219 \times 10^{-11}` J/m speed Å/ps :math:`100` m/s - mass u :math:`1.66053906660(50) \times 10^{-27}` kg + mass u :math:`1.66053892103219 \times 10^{-27}` kg angle degrees :math:`\frac{\pi}{180}` rad =========== ============== =============================================== +MDAnalysis units are currently based on the NIST `CODATA 2010`_ values for +physical constants. The unit of mass is not explicitly used but implicit in the +units for force and energy via Avogadro's constant :math:`6.02214129(27) \times +10^{23}\,\mathrm{mol}^{-1}` (in :data:`MDAnalysis.units.constants`). The excess +precision in the table is due to the use of the inverse of Avogadro's constant +and listing all available digits of the numerical calculation. + +.. _`CODATA 2010`: + https://physics.nist.gov/cuu/Constants/ArchiveASCII/allascii_2010.txt + Unit conversion =============== From f7406f7565c8bcbc65634017a72c74a851388178 Mon Sep 17 00:00:00 2001 From: Oliver Beckstein Date: Thu, 3 Sep 2026 09:24:50 -0700 Subject: [PATCH 2/2] fix whitespace --- doc/source/units.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/doc/source/units.rst b/doc/source/units.rst index 00434f209..31354c324 100644 --- a/doc/source/units.rst +++ b/doc/source/units.rst @@ -41,7 +41,7 @@ and listing all available digits of the numerical calculation. .. _`CODATA 2010`: https://physics.nist.gov/cuu/Constants/ArchiveASCII/allascii_2010.txt - + Unit conversion ===============