# potfit wiki

open source force-matching

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# Units

potfit does not need a particular system of units. It can work with any system. The units used by potfit are implicitly defined in the configuration and potential files, and possibly by certain parameters specifying the potential.

The reference configuration file contains atom positions, which implicitly defines the unit of length. The interaction potential implicitly makes use of a length unit and an energy unit. Of course, this length unit must be the same as for the configuration file. The two units of length, and energy determine other units - like force and pressure - which are derived from them. The temperature in simulated annealing has the same dimension as the sum of squares - none at all.

### Example

If the length unit is $$1~\unicode{x212B} = 1\cdot 10^{-10}~\mathrm{m},$$ and the energy unit is $$1~\mathrm{eV} = 1.602\cdot 10^{-19}~\mathrm{J}$$ (which corresponds to $11594~\mathrm{K}$), then the unit of pressure is $$160.2~\mathrm{GPa} = 1602~\mathrm{kbar},$$ and the unit of force is $$1~\frac{\mathrm{eV}}{\unicode{x212B}} = 1.602\cdot 10^{-9}~\mathrm{N}.$$