Clarify dt heuristics

examples/03_LLD_CoRh2O4.jl

@@ -27,12 +27,12 @@ sys = resize_supercell(sys, (10, 10, 10))
 
 # Use the stochastic Landau-Lifshitz dynamics to thermalize system into
 # equilibrium at finite temperature via the [`Langevin`](@ref) dynamics. The
-# timestep ``Δt`` controls integration accuracy. It should be inversely
-# proportional to the largest effective field in the system. For CoRh₂O₄, this
-# is the antiferromagnetic exchange ``J`` times the spin magnitude. The
-# dimensionless parameter ``λ`` determines the magnitude of Langevin noise and
-# damping terms. A reasonable choice is `λ = 0.2`. The temperature `kT` is
-# linked to the magnitude of the Langevin noise term via a
+# timestep ``Δt`` controls integration accuracy. In `:dipole` mode, it should be
+# inversely proportional to the largest effective field in the system. For
+# CoRh₂O₄, this is the antiferromagnetic exchange ``J`` times the spin magnitude
+# ``S=3/2``. The dimensionless parameter ``λ`` determines the magnitude of
+# Langevin noise and damping terms. A reasonable choice is `λ = 0.2`. The
+# temperature `kT` is linked to the magnitude of the Langevin noise term via a
 # fluctuation-dissipation theorem.
 
 Δt = 0.05/abs(J*S)   # Integration timestep

examples/04_GSD_FeI2.jl

@@ -80,16 +80,16 @@ sys
 # configurations from the thermal equlibrium.
 #
 # The [`Langevin`](@ref) integrator requires several parameters. The timestep
-# ``Δt`` controls integration accuracy. It should be inversely proportional to
-# the largest effective field in the system. For FeI₂, this is the easy-axis
-# anisotropy ``D`` times the spin magnitude ``S = 1``. The dimensionless
-# parameter ``λ`` determines the magnitude of Langevin noise and damping terms.
-# A reasonable choice is `λ = 0.2`. The temperature `kT` is linked to the
-# magnitude of the noise via a fluctuation-dissipation theorem.
-
-Δt = 0.05/abs(D*1) # Integration timestep
-λ  = 0.2           # Dimensionless damping time-scale
-kT = 0.2           # Temperature in meV
+# ``Δt`` controls integration accuracy. In `:SUN` mode, it should be inversely
+# proportional to the largest energy scale in the system. For FeI₂, this is the
+# easy-axis anisotropy ``D`` times the spin magnitude squared, ``S^2 = 1``. The
+# dimensionless parameter ``λ`` determines the magnitude of Langevin noise and
+# damping terms. A reasonable choice is `λ = 0.2`. The temperature `kT` is
+# linked to the magnitude of the noise via a fluctuation-dissipation theorem.
+
+Δt = 0.05/abs(D)  # Integration timestep
+λ  = 0.2          # Dimensionless damping time-scale
+kT = 0.2          # Temperature in meV
 langevin = Langevin(Δt; kT, λ);
 
 # Langevin dynamics can be used to search for a magnetically ordered state. For