.. -*- coding: utf-8 -*- .. _units: =================== Units and constants =================== The units of MDAnalysis trajectories are the **Å** (**ångström**) for **length** and **ps** (**picosecond**) for **time**. Regardless of how the original MD format stored the trajectory data, MDAnalysis converts it to MDAnalysis units when reading the data in, and converts back when writing the data out. Analysis classes generally also use these default units. Exceptions to the default units are always noted in the documentation; for example, mass densities can be given in :math:g/cm^3. Other base units are listed in the table :ref:table-baseunits. .. _table-baseunits: .. Table:: Base units in MDAnalysis =========== ============== =============================================== Quantity Unit SI units =========== ============== =============================================== length Å :math:10^{-10} m time ps :math:10^{-12} s energy kJ/mol :math:1.66053892103219 \times 10^{-21} J 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 angle degrees :math:\frac{\pi}{180} rad =========== ============== =============================================== Unit conversion =============== Quantities can be converted from units with :func:~MDAnalysis.units.convert. :func:~MDAnalysis.units.convert simply multiplies the initial quantity with a precomputed conversion factor, as obtained from :func:~MDAnalysis.units.get_conversion_factor. The computed conversion factors for each quantity type are stored in :mod:MDAnalysis.units and shown below. Constants ========= .. include:: generated/units_table.txt