# Units¶

The unit system used internally by Lumol is the following:

• Angstrom (A) for distances;
• Femtosecond (fs) for time;
• Unified atomic mass unit (u or Da) for mass;
• Kelvin (K) for temperature;
• Number of particles for quantity of matter;
• Radian (rad) for angles;

Any other internal unit is derived from this set:

• The internal unit of energy is u A^2 fs^-2;
• The internal unit of force is u A fs^-2;
• The internal unit of pressure is u A^-1 fs^-2;
• etc.

For convenience Lumol provides convertion facilities for any value in these internal unit to any others units. The following table lists available units that can be converted:

Quantity Accepted units
Distance A, Å, nm, pm, fm, m, bohr
Time fs, ps, ns
Mass u, Da, kDa, g, kg
Matter mol
In the input files, the units are specified as strings, and must be spelled exactly as in the above table. They can be combined with other units using * for multiplication, / for division, and ^ for exponentiation. Parentheses can be used to group sub-units together. Some valid unit strings are kcal/mol, (J / mol) * A^-2, and m*fs^-1.