diff --git a/src/MolecularDockingKit/combine.py b/src/MolecularDockingKit/combine.py
index d5e589d..372d8f2 100644
--- a/src/MolecularDockingKit/combine.py
+++ b/src/MolecularDockingKit/combine.py
@@ -1,50 +1,62 @@
-import os, glob, sys
-from rdkit import Chem
-from multiprocessing import Pool
+import os
+import sys
 from rdkit import Chem
 from rdkit.Chem import AllChem
 import numpy as np
 
-###########################################################################
-#                                                                         #
-# This program takes in one argument for the file index for the file      #
-# inside the directory called moleculeLists.txt named something like      #
-# file000, file001 etc. that contains the names of five drugs. The energy #
-# calculations for these drugs is submitted together. This way, I         #
-# parallelize the calculations with brute force separate job submitions.  #
-#                                                                         #
-###########################################################################
-
-molList = open('moleculeLists/fiveSplits/file' + sys.argv[1] + '.txt', 'r').readlines()
-molList = [mol.strip() for mol in molList]
-enzymeFile = '../../3sxr_dasatinib_removed.pdb'
-
-os.chdir('rDock_inputs/')
-for ligandName in molList:
-    os.chdir(ligandName)
-    suppl = Chem.SDMolSupplier(ligandName + '_docking_out_sorted.sd')
-    mols = [x for x in suppl]
-    m1 = mols[-1]
-    m2 = Chem.rdmolfiles.MolFromPDBFile(enzymeFile)
+def calculate_energy(file_index: str) -> None:
+    """
+    Perform energy calculations for a list of drugs specified in the file indexed by `file_index`.
+
+    Args:
+        file_index (str): Index of the file containing the list of drugs.
+
+    Returns:
+        None
+    """
+    mol_list = open(f'moleculeLists/fiveSplits/file{file_index}.txt', 'r').readlines()
+    mol_list = [mol.strip() for mol in mol_list]
+    enzyme_file = '../../3sxr_dasatinib_removed.pdb'
 
-    #Generating the ligand + protein geometry
-    combo = Chem.CombineMols(m1, m2)
-    combo = Chem.AddHs(combo, addCoords=True)
-    Chem.rdmolfiles.MolToPDBFile(combo, 'combo.pdb')
+    os.chdir('rDock_inputs/')
+    for ligand_name in mol_list:
+        os.chdir(ligand_name)
+        m1, m2 = load_molecules(ligand_name, enzyme_file)
 
-    #Calculating the energy for the (ligand + protein) geometry
-    #As I say in the other document, xtb did not work and I ended up using rdkit
-    #for this step
-    #os.system('xtb --gfnff combo.xyz > combo.log')
-    res = AllChem.MMFFOptimizeMoleculeConfs(combo, maxIters=0, numThreads=0)
+        # Generate the ligand + protein geometry
+        combo = Chem.CombineMols(m1, m2)
+        combo = Chem.AddHs(combo, addCoords=True)
+        Chem.rdmolfiles.MolToPDBFile(combo, 'combo.pdb')
 
-    #Calculating the energies for the ligand only geometry
-    m1 = Chem.AddHs(m1, addCoords=True)
-    res1 = AllChem.MMFFOptimizeMoleculeConfs(m1, maxIters=0, numThreads=0)
+        # Calculate the energy for the (ligand + protein) geometry
+        res = AllChem.MMFFOptimizeMoleculeConfs(combo, maxIters=0, numThreads=0)
 
-    #Saving the energies for the (ligand + protein) and the ligand only geometry in a file
-    np.savetxt('energies.txt', [res[0][1], res1[0][1]])
+        # Calculate the energies for the ligand only geometry
+        res1 = AllChem.MMFFOptimizeMoleculeConfs(m1, maxIters=0, numThreads=0)
+
+        # Save the energies for the (ligand + protein) and the ligand only geometry in a file
+        np.savetxt('energies.txt', [res[0][1], res1[0][1]])
+        os.chdir('../../../')
     os.chdir('../../../')
-os.chdir('../../../')
 
+def load_molecules(ligand_name: str, enzyme_file: str) -> tuple[Chem.Mol, Chem.Mol]:
+    """
+    Load ligand and enzyme molecules from SD and PDB files, respectively.
+
+    Args:
+        ligand_name (str): Name of the ligand molecule.
+        enzyme_file (str): Path to the enzyme PDB file.
+
+    Returns:
+        Tuple containing the ligand and enzyme molecules.
+    """
+    suppl = Chem.SDMolSupplier(f'{ligand_name}_docking_out_sorted.sd')
+    mols = [x for x in suppl]
+    m1 = mols[-1]
+    m2 = Chem.rdmolfiles.MolFromPDBFile(enzyme_file)
+    return m1, m2
 
+# Example usage
+if __name__ == "__main__":
+    file_index = sys.argv[1]
+    calculate_energy(file_index)