Unit system#
In most cases, the SI unit system is frequently chosen to describe physical quantities. However, the scale of MD simulation is much smaller than the SI unit system. In this case, using the SI system to perform numerical operations like addition yields big numerical errors.
To ensure the convergence and accuracy of the simulation, most MD packages choose a new unit system that is comparable to the atomic scale. Here, we list the default unit system used in MDPy.
Dimension |
SI |
MDPy |
SI/MDPy |
|---|---|---|---|
Length |
m |
angstrom |
\(10^{10}\) |
Time |
s |
femtosecond |
\(10^{12}\) |
Mass |
kg |
dalton |
\(6.023\times10^{26}\) |
Temperature |
kelvin |
kelvin |
\(1\) |
Charge |
coulomb |
e |
\(6.24\times10^{18}\) |
Amount of substance |
mol |
mol |
\(1\) |
Other units, such as energy and force, are derived from the multiplication and division of the basic units.
Tip
To get more information of unit system of MDPy, check tutorial: How to use mdpy.unit package