Update src/nmreval/models/temperature.py

Add Tanaka model

src/nmreval/models/temperature.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import numpy as np
 
 from ..utils.constants import kB
@@ -72,3 +74,25 @@ class Ecoop:
         ec = e_infty * np.exp(-mu * (x - ta) / e_infty)
 
         return tau0 * np.exp((e_infty + ec) / x)
+
+
+class Tanaka:
+    name = 'Tanaka two-state model'
+    type = 'Temperature'
+    equation = r'\tau_0 exp[(E_{a}^{f} + (E_{a}^{s}-E_{a}^{f})[1/(1+exp[(\DeltaE-T \Delta\sigma)/(k_{}B T)])]/(k_{B} T)]'
+    params = [r'\tau_{0}', 'E_{a}^{f}', 'E_{a}^{s}', r'\DeltaE', r'\Delta\sigma']
+    bounds = [(0, None), (0, None), (0, None), (None, 0), (None, 0)]
+    choices = [('temperature', 'temp_axis', {'T': 'T', '1000 K/T': '1000/T'})]
+
+    @staticmethod
+    def func(x, tau0: float, ea_f: float, ea_s: float, e_D: float, sigma_D: float, temp_axis: str = 'T'):
+
+        if temp_axis == '1000/T':
+            x = 1000/x
+
+        kT = kB * x
+
+        exponent = 1 / (1 + np.exp((e_D - x * sigma_D) / kT))
+
+        return tau0 * np.exp((ea_f + (ea_s - ea_f) * exponent) / kT)
+