Fix carrier diffusion, code cleanup and speedup

Author: contuandrea

examples/example_config.cfg

@@ -46,7 +46,7 @@ InputData:
         #number of time steps in the simulation, integer. 
 	#NEEDED
         #it can be an array (e.g. [400,600]). In this case simulations will be performed with all the values
-        steps = 100;
+        steps = 600;
 
         #time step in seconds, double. NEEDED
         #it can be an array (e.g. [1e-11,1e-13,1e-14]). In this case simulations will be performed with all the values
@@ -108,7 +108,7 @@ InputData:
         #it can be an array
         particles = 20000; #it cannot be -1 in this case since no input file is provided
 
-        T=0.;
+        T=300.;
 
         Xshift = 2.;
         Yshift = 2.;