diff --git a/README.md b/README.md
index 6b21ef5..cb0b357 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,7 @@ pip install matplotlib
 **radiation_fields.py** :  
 *Description* :  
 This program calculates the scaling factor of the radiation field G0 relative 
-to the data of an object or a set of objects radiating for given distances
+to the spectrum of an object or a set of objects radiating for given distances
 A file containing my G0 values with the associated distance will then be created
 
 *Input parameters* :  
@@ -35,8 +35,7 @@ the part of the program executed will be independent of them
 
 **three_levels_model.py** :  
 *Description* :  
-This program seeks to calculate how a neutral gas subjected to a radiation field 
-is heated, involving PAHs in the ionization of the gas. The expressions used are based on the model with 3 energy levels of the molecule, going from the neutral molecule (charge state Z=0) to the dication (charge state Z=2) by ionization.  
+This main program computes the photoelectric heating rate and efficiency by PAHs. The expressions used are based on the model with 4 charge states of the molecule, going from the anion molecule (charge state Z=-1) to the dication (charge state Z=2) by ionization.  
 
 *Input parameters* :  
      filename : str,   
@@ -56,12 +55,9 @@ is heated, involving PAHs in the ionization of the gas. The expressions used are
         ISRF : bool,   
             Interstellar Radiation Field; if true, then the filename is a file for ISRF
             if false, the radiation field of a star is studied (default: False)  
-            
-**four_levels_model.py** :  
-*Description* :  
-This program does the same thing and has the same parameters as the program three_levels_model.py, the difference being that we add expressions related to the 4 energy levels model. This model consists in taking into account the anions, i.e. the PAHs in a charge state Z = -1.
+        
+        This program uses radiations_fields.py.   
 
-These last two programs use the parameters returned by radiations_fields.py in its calculations
 
 ## Useful files
 
--
libgit2 0.21.2