import json
       import os
       import sys

       f=open('sim.json')              #open the sim.json file
       lines=f.readlines()
       f.close()
       lines="".join(lines)    #convert the text to a python json object
     data = json.loads(lines)

     #Edit a value (use firefox as a json viewer
     # to help you figure out which value to edit)
     # this time we are editing the mobility of layer 1
     data['epitaxy']['segment1']['shape_dos']['mue_y']=1.0


     #convert the json object back to a string
     jstr = json.dumps(data, sort_keys=False, indent='\t')

     #write it back to disk
     f=open('sim.json',"w")
     f.write(jstr)
     f.close()

     #run the simulation using oghma_core
     os.system("oghma_core.exe")

f=open('sim_info.dat')
lines=f.readlines()
f.close()
lines="".join(lines)
data = json.loads(lines)

f=open('out.dat',"a")
f.write(str(data["Voc"])+"\n");
f.close()

       import json
       import os
       import shutil

       # The script must be started in the base simulation directory
       # (i.e. the directory containing the reference sim.json).
       base_dir = os.getcwd()

       mobilities = [1e-5, 1e-6, 1e-7, 1e-8]

       for mu in mobilities:
           # Create a directory name that is easy to read and sorts nicely
           run_dir = os.path.join(base_dir, f"mu_{mu:.0e}")
           os.makedirs(run_dir, exist_ok=True)

           # Copy the base sim.json into the run directory
           src_sim = os.path.join(base_dir, "sim.json")
           dst_sim = os.path.join(run_dir, "sim.json")
           shutil.copyfile(src_sim, dst_sim)

           # Load the copied sim.json and edit the mobility in THAT copy
           f = open(dst_sim)
           lines = f.readlines()
           f.close()
           lines = "".join(lines)
           data = json.loads(lines)

           # Edit a value: set the mobility for the first device layer
           data['epitaxy']['segment1']['shape_dos']['mue_y'] = mu

           jstr = json.dumps(data, sort_keys=False, indent='\t')
           f = open(dst_sim, "w")
           f.write(jstr)
           f.close()

           # Change into the run directory and execute the solver there
           os.chdir(run_dir)

           # If your command is "augment.nano" instead, replace the string below.
           os.system("oghma_core.exe")

           # Return to the base directory for the next run
           os.chdir(base_dir)

       import json
       import os

       # Optional: plotting (requires matplotlib)
       import matplotlib.pyplot as plt

       base_dir = os.getcwd()

       # Mobilities must match the run directories you generated earlier
       mobilities = [1e-5, 1e-6, 1e-7, 1e-8]

       inv_mu = []
       vocs = []

       for mu in mobilities:
           run_dir = os.path.join(base_dir, f"mu_{mu:.0e}")
           info_path = os.path.join(run_dir, "sim_info.dat")

           # Read the JSON output file and extract Voc
           f = open(info_path)
           lines = f.readlines()
           f.close()
           lines = "".join(lines)
           data = json.loads(lines)

           voc = data["Voc"]

           inv_mu.append(1.0 / mu)
           vocs.append(voc)

       # Write a small summary table to disk
       out = open("voc_vs_inv_mobility.dat", "w")
       out.write("# inv_mobility(1/mu)    Voc(V)\n")
       for x, y in zip(inv_mu, vocs):
           out.write(f"{x:.6e}    {y}\n")
       out.close()

       # Plot Voc against inverse mobility
       plt.plot(inv_mu, vocs, "o-")
       plt.xlabel("Inverse mobility (1/μ)")
       plt.ylabel("Open-circuit voltage Voc (V)")
       plt.title("Voc vs inverse mobility")
       plt.grid(True)
       plt.tight_layout()
       plt.show()