# Units¶

## Overview¶

Simulations in Dash can use either real or reduced/Lennard-Jones units. This is specified by updating the units attribute of the state. Lennard-Jones units are the default, so it is imporant to select the desired units before setting simulation parameters.

## Setting Real Units¶

Dash can be set to real (or LJ) units by invoking the setReal() (or setLJ()) method of the units property in the state. Real units are the following:

Energy: kcal/mol

Distance: Angstroms

Time: femptoseconds

Temperature: Kelvin

Mass: atomic mass units (amu)

Charge: electronic charge

Pressure: atmospheres

Example

The following code sets the units of a simulation to real units and then back to reduced units.

Setting the units also sets the timestep to default values of 1.0 fs for real units and 0.005 for LJ units.

#set real units
state.units.setReal()

state.units.setLJ()