Units are a key concept in ATK. All parameters that correspond to physical quantities, such as lengths, energies, voltages, etc, should be specified with an explicit unit. Similarly, all results returned from calculations in ATK also contain an explicit unit.

All physical quantities (that is, objects associated with a unit) have two query methods:

a = 5*Angstrom
print a.inUnitsOf(nanoMeter)

generates

0.5

while

print a.convertTo(nanoMeter)

gives

0.5 nm

Physical quantities can be transformed with x**n, for instance

a = 2. * Meter *Second**-2
v = (2 * a * (1*Meter))**0.5
print v
    

gives

2.0 m/s 

Specify inverse units by using the exponent operator **, i.e.

f = 2.2/Second
print f.inUnitsOf(Second**-1)

The following units are made available when importing NanoLanguage:

Units are attached to values by multiplication. Thus, to specify a length of 5 Bohr, use

a = 5*Bohr

By printing the value of the variable a, the unit will automatically be displayed also:

print a

gives

5.0 Bohr

Units can also be composite. The unit for force is Newton, which is Joule per Meter. This is a rather awkward unit for nanoscale calculations, where instead something like electron volt per nm makes more sense. Any energy divided by a length is however a valid force unit, so to specify a force, write

F = 5*eV/Bohr

Now, multiply this by a length again and the result will be an energy:

b = F*5*Bohr
print b

generates the output

25*eV

Some unit abbreviations are only available with the Units prefix

b = 5.1*Units.Ry
print b

gives

5.1 Rydberg

Units which by default are specified without a prefix, can also be given with a prefix, for example

b = 5.1*Rydberg
c = 5.1*Units.Rydberg