diff --git a/cpp/full_code/ornstein_uhlenbeck_process.cpp b/cpp/full_code/ornstein_uhlenbeck_process.cpp
index f8266fdb391d253026abaa2fe97bc263c49da0d2..f3955eccd9b59067d6fdab8d08cc631313e92ff3 100644
--- a/cpp/full_code/ornstein_uhlenbeck_process.cpp
+++ b/cpp/full_code/ornstein_uhlenbeck_process.cpp
@@ -138,11 +138,11 @@ void ornstein_uhlenbeck_process<rnumber,be>::initialize_B()
                 else
                 {
                     //sigma =
-                     //   sqrt(4*this->gamma(kabs)*this->energy(kabs)
-                       // /this->kk->nshell[(int)(kabs/this->kk->dk)]);
+                    //    sqrt(4*this->gamma(kabs)*this->energy(kabs)
+                    //    /this->kk->nshell[(int)(kabs/this->kk->dk)]);
                     sigma =
                         sqrt(4*this->gamma(kabs)*this->energy(kabs)
-                        /this->kk->nshell[(int)(kabs/this->kk->dk)]);
+                        /(4*M_PI*ksqu));
                 }
 
                 for(int i=0;i<3;i++) {