Added new function to calculate freezing point depression for different aqueous solutions.

Calculations/formulas.py

@@ -1903,3 +1903,50 @@ def find_half_collection_efficiency(efficiency: npt.ArrayLike) -> tuple[int, int
     first_half_point = np.abs(lower_array - 0.5).argmin()
     second_half_point = np.abs(upper_array - 0.5).argmin()
     return (first_half_point, second_half_point+max_value)
+
+
+def freezing_point_depression(molatility_of_salt: float, salt: str = 'NaCl') -> float:
+    """
+    Function to calculate the freezing point depression of aqueous solutions
+    containing four different salts (NaCl, KCl, LiCl, MgCl2) using fit parameters
+    from _[1]
+
+    Parameters
+    ----------
+    molatility_of_salt : float
+        DESCRIPTION.
+    salt : str, optional
+        Salt. The default is 'NaCl'.
+
+    Returns
+    -------
+    float
+        Freezing point depression in K.
+
+    References
+    ----------
+    [1] Cintia P. Lamas, Carlos Vega, Eva G. Noya; Freezing point depression
+    of salt aqueous solutions using the Madrid-2019 model. J. Chem. Phys.
+    7 April 2022; 156 (13): 134503. https://doi.org/10.1063/5.0085051
+
+    """
+    m = molatility_of_salt  # mol/kg
+    match salt:
+        case 'NaCl':
+            v = 2
+            b = -1.639
+            c = 0.683
+        case 'KCl':
+            v = 2
+            b = -1.565
+            c = 0.665
+        case 'LiCl':
+            v = 2
+            b = -2.315
+            c = 1.605
+        case 'MgCl2':
+            v = 3
+            b = -6.859
+            c = 5.676
+    delta_T = -v * 1.998 * m - b * m**(3/2) - c * m**2
+    return delta_T