From 43aade957ecf9b704044b75635a1c961ac0abd01 Mon Sep 17 00:00:00 2001
From: Kipton Barros <kbarros@gmail.com>
Date: Thu, 25 Jul 2024 13:59:08 -0600
Subject: [PATCH] Update to units

---
 src/Units.jl | 56 +++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 38 insertions(+), 18 deletions(-)

diff --git a/src/Units.jl b/src/Units.jl
index e97364d77..5e957cf97 100644
--- a/src/Units.jl
+++ b/src/Units.jl
@@ -1,62 +1,82 @@
-# Angstrom in selected length unit
 const angstrom_in = Base.ImmutableDict(
     :angstrom => 1.0, # == Å / Å
     :nm => 0.1,       # == Å / nm
 )
 
-# meV in selected energy unit
 const meV_in = Base.ImmutableDict(
     :meV => 1.0,                   # meV / meV
     :K   => 801088317/69032450,    # meV / kB K
     :THz => 267029439/1104345025,  # meV / h THz
+    :inverse_cm => 6621486190496429/53405887800000000, # meV / (h c / cm)
     :T   => 17.275985474052367519, # meV / μB T
 )
 
+const unit_strs = Base.ImmutableDict(
+    :angstrom => "Å",
+    :nm => "nm",
+    :meV => "meV",
+    :K   => "K",
+    :THz => "THz",
+    :inverse_cm => "cm⁻¹",
+    :T   => "μB T",
+    :vacuum_permeability => "μ0 μB²",
+)
 
 """
     Units(energy, length=:angstrom)
 
 Physical constants in units of reference `energy` and `length` scales. Possible
-lengths are `[:angstrom, :nm]` and possible energies are `[:meV, :K, :THz]`.
-Kelvin is converted to energy via the Boltzmann constant ``k_B``. Similarly,
-hertz is converted via the Planck constant ``h``, and tesla (field strength) via
-the Bohr magneton ``μ_B``. For a given `Units` system, one can access length
-scales (`angstrom`, `nm`) and energy scales (`meV`, `K`, `THz`, `T`).
+lengths are `[:angstrom, :nm]` and possible energies are `[:meV, :K, :THz,
+:inverse_cm, :T]`. Kelvin is converted to energy via the Boltzmann constant
+``k_B``. Similarly, hertz is converted via the Planck constant ``h``, inverse cm
+via the speed of light ``c``, and tesla (field strength) via the Bohr magneton
+``μ_B``. For a given `Units` system, one can access any of the length and energy
+scale symbols listed above.
 
 # Examples
 
 ```julia
-# Create a unit system where energies are measured in meV
+# Unit system with [energy] = meV and [length] = Å
 units = Units(:meV)
 
-# Use the Boltzmann constant ``k_B`` to convert 1 kelvin into meV
+# Use the Boltzmann constant kB to convert 1 kelvin into meV
 @assert units.K ≈ 0.0861733326
 
-# Use the Planck constant ``h`` to convert 1 THz into meV
+# Use the Planck constant h to convert 1 THz into meV
 @assert units.THz ≈ 4.135667696
 
-# Use the Bohr magneton ``μ_B`` to convert 1 tesla into meV
+# Use the constant h c to convert 1 cm⁻¹ into meV
+@assert units.inverse_cm ≈ 0.1239841984
+
+# Use the Bohr magneton μB to convert 1 tesla into meV
 @assert units.T ≈ 0.05788381806
 
-# The physical constant ``μ_0 μ_B²`` in units of ų meV.
+# The physical constant μ0 μB² in units of ų meV.
 @assert u.vacuum_permeability ≈ 0.6745817653
 ```
 """
-struct Units{E, L}
+struct Units
+    energy::Symbol
+    length::Symbol
+
     function Units(energy, length=:angstrom)
         length in keys(angstrom_in) || error("`length` must be one of $(keys(angstrom_in))")
         energy in keys(meV_in) || error("`energy` must be one of $(keys(meV_in))")
-        return new{energy, length}()
+        return new(energy, length)
     end
 end
 
-function Base.getproperty(u::Units{E, L}, name::Symbol) where {E, L}
+function Base.getproperty(u::Units, name::Symbol)
+    if name in (:energy, :length)
+        return getfield(u, name)
+    end
+
     if name in (:meV, :K, :THz, :T)
-        return meV_in[E] / meV_in[name]
+        return meV_in[u.energy] / meV_in[name]
     end
     
     if name in (:angstrom, :nm)
-        return angstrom_in[L] / angstrom_in[name]
+        return angstrom_in[u.length] / angstrom_in[name]
     end
 
     if name == :vacuum_permeability
@@ -64,5 +84,5 @@ function Base.getproperty(u::Units{E, L}, name::Symbol) where {E, L}
         return 0.6745817653324668 * u.angstrom^3 * u.meV
     end
 
-    error("type Units has no constant $name")
+    error("Unknown unit :$name")
 end