Correct a sign error in the derivative of the dielectric profiles

Author: robertodr

src/green/dielectric_profile/OneLayerErf.hpp

@@ -65,7 +65,7 @@ class OneLayerErf
      *  \param[in] point where to evaluate the derivative
      */
     double derivative(double point) const {
-        double factor = (epsilon1_ - epsilon2_) / (width_ * std::sqrt(M_PI));
+        double factor = (epsilon2_ - epsilon1_) / (width_ * std::sqrt(M_PI));
         double t = (point - center_) / width_;
         double val = std::exp(-std::pow(t, 2));
         return (factor * val); //first derivative of epsilon(r)

src/green/dielectric_profile/OneLayerTanh.hpp

@@ -64,7 +64,7 @@ class OneLayerTanh
      *  \param[in] point where to evaluate the derivative
      */
     double derivative(double point) const {
-        double factor = (epsilon1_ - epsilon2_) / (2.0 * width_);
+        double factor = (epsilon2_ - epsilon1_) / (2.0 * width_);
         double tanh_r = std::tanh((point - center_) / width_);
         return (factor * (1 - std::pow(tanh_r, 2))); //first derivative of epsilon(r)
     }