Not fully conservative but works

The code is still not fully conservative in intra-species collisions
(small error) but at least now is working.

I have to test species with different weight.

I have to implement a fully conservation for intra-species.

src/modules/mesh/moduleMesh.f90

@@ -1069,6 +1069,7 @@ MODULE moduleMesh
             deltaW_par_square = SQRT(AW * GlW * tauMin)*randomMaxwellian()
             deltaW_per_square = SQRT(AW * HlW * tauMin)*randomMaxwellian()
 
+            !Random angle to distribute perpendicular change in velocity
             theta_per = PI2*random()
 
             !Change W
@@ -1076,9 +1077,10 @@ MODULE moduleMesh
             W(2) =         deltaW_per_square * SIN(theta_per)
             W(3) = normC + deltaW_par + deltaW_par_square
 
-            !Change particle velocity
+            !Update particle velocity and return to laboratory frame
             partTemp%part%v = velocity + MATMUL(rotation, W)
                                                
+            !Move to the next particle in the list
             partTemp => partTemp%next
 
           END DO

src/modules/moduleCoulomb.f90

@@ -59,8 +59,10 @@ MODULE moduleCoulomb
       self%sp_i => species(i)%obj
       self%sp_j => species(j)%obj
 
-      self%one_plus_massRatio_ij = 1.D0 + (self%sp_i%weight*self%sp_i%m)/(self%sp_j%weight*self%sp_j%m)
+      self%one_plus_massRatio_ij = 1.D0 + self%sp_i%m/self%sp_j%m
 
+      Z_i = 0.D0
+      Z_j = 0.D0
       SELECT TYPE(sp => self%sp_i)
       TYPE IS (speciesCharged)
         Z_i = sp%q