UnitfulAtomic

This package extends the Unitful.jl package to facilitate working with atomic units.

Functions

This package provides three functions that enable easy conversion from and to Hartree atomic units:

aunit(x) returns the appropriate atomic unit for x, where x can be a Unitful.Quantity, Unitful.Units, or Unitful.Dimensions:
```
julia> aunit(2.3u"cm")
a₀

julia> aunit(u"T")
ħ a₀^-2 e^-1
```
auconvert can be used to convert from and to atomic units. It has two methods:
- auconvert(x::Unitful.Quantity) converts a quantity to the appropriate atomic unit:
```
julia> auconvert(13.6u"eV")
0.499790781587053 Eₕ

julia> auconvert(20u"nm")
377.94522492515404 a₀
```
- auconvert(u::Unitful.Units, x::Number) interprets x as a quantity in atomic units and converts it to the unit u:
```
julia> auconvert(u"eV", 1)  # convert 1 Eₕ to eV
27.211386246088992 eV

julia> auconvert(u"m", 1)   # convert 1 a₀ to m
5.29177210903e-11 m
```
austrip(x::Unitful.Quantity) converts a quantity to the appropriate atomic unit and then strips the units. This is equivalent to Unitful.ustrip(auconvert(x)):
```
julia> austrip(13.6u"eV")
0.499790781587053

julia> austrip(20u"nm")
377.94522492515404
```

Defined units

The package defines the following atomic units (suffixed with _au), from which all other atomic units are derived:

me_au (printed as mₑ): the electron rest mass.
e_au (printed as e): the elementary charge.
ħ_au (printed as ħ): the reduced Planck constant.
k_au (printed as k): the Boltzmann constant.
a0_au (printed as a₀): the Bohr radius. The alias bohr can be used instead of a0_au.
Eh_au (printed as Eₕ): the Hartree energy. The alias hartree can be used instead of Eh_au.

Furthermore, this package defines some units that are not atomic units, but are common in atomic physics:

Ry: the Rydberg energy Ry = h*c*R∞ = Eₕ/2, see Rydberg constant.
μ_N: the nuclear magneton.