code: private HashMap<String, Integer> getWisley_2000() {
          HashMap<String, Integer> map = new HashMap<String, Integer>();
  
          map.put("C", 156);
          map.put("H", 180);
          map.put("N", 20);
          map.put("O", 40);
          map.put("P", 9);
          map.put("S", 14);
          map.put("F", 48);
          map.put("Cl", 12);
          map.put("Br", 10);
          map.put("Si", 15);
  
          return map;
      }
docs: Get the map linking the symbol of the element and number maximum of occurrence.
  For the analysis with the Wisley database and mass lower than 2000 Da.
  
  @return The HashMap of the symbol linked with the maximum occurrence