diff --git a/src/GW/GW_ppBSE_static_kernel_C.f90 b/src/GW/GW_ppBSE_static_kernel_C.f90
index 534654c..2df0025 100644
--- a/src/GW/GW_ppBSE_static_kernel_C.f90
+++ b/src/GW/GW_ppBSE_static_kernel_C.f90
@@ -31,6 +31,8 @@ subroutine GW_ppBSE_static_kernel_C(ispin,eta,nBas,nC,nO,nV,nR,nS,nVV,lambda,ERI
   integer                       :: a0, aa
 
   double precision, allocatable :: Om_tmp(:)
+  double precision, allocatable :: tmp_m(:,:,:)
+  double precision, allocatable :: tmp(:,:,:,:)
 
 ! Output variables
 
@@ -46,19 +48,27 @@ subroutine GW_ppBSE_static_kernel_C(ispin,eta,nBas,nC,nO,nV,nR,nS,nVV,lambda,ERI
     lambda4 = 4.d0 * lambda
     eta2 = eta * eta
 
-    allocate(Om_tmp(nS))
+    allocate(tmp_m(nBas,nBas,nS))
+    allocate(tmp(nBas,nBas,nBas,nBas))
 
-    !$OMP PARALLEL DEFAULT(NONE) PRIVATE(m) SHARED(nS, eta2, Om, Om_tmp)
-    !$OMP DO
     do m = 1, nS
-      Om_tmp(m) = Om(m) / (Om(m)*Om(m) + eta2)
+      eps = Om(m) / (Om(m)*Om(m) + eta2)
+      do c = 1, nBas
+        do a = 1, nBas
+          tmp_m(a,c,m) = eps * rho(a,c,m)
+        enddo
+      enddo
     enddo
-    !$OMP END DO
-    !$OMP END PARALLEL
 
-    !$OMP PARALLEL DEFAULT(NONE)                              &
-    !$OMP          PRIVATE(a, b, aa, ab, c, d, cd, m, tmp_ab) &
-    !$OMP          SHARED(nO, nBas, nR, nS, a0, lambda4, Om_tmp, rho, KC)
+    call dgemm("N", "T", nBas*nBas, nBas*nBas, nS, 1.d0,       &
+               tmp_m(1,1,1), nBas*nBas, rho(1,1,1), nBas*nBas, &
+               0.d0, tmp(1,1,1,1), nBas*nBas)
+
+    deallocate(tmp_m)
+
+    !$OMP PARALLEL DEFAULT(NONE)                           &
+    !$OMP          PRIVATE(a, b, aa, ab, c, d, cd, tmp_ab) &
+    !$OMP          SHARED(nO, nBas, nR, nS, a0, lambda4, tmp, KC)
     !$OMP DO
     do a = nO+1, nBas-nR
       aa = a0 * (a - nO - 1) - (a - nO - 1) * (a - nO) / 2 - nO
@@ -75,13 +85,7 @@ subroutine GW_ppBSE_static_kernel_C(ispin,eta,nBas,nC,nO,nV,nR,nS,nVV,lambda,ERI
           do d = c, nBas-nR
             cd = cd + 1
 
-            KC(ab,cd) = 0d0
-            do m = 1, nS
-              KC(ab,cd) = KC(ab,cd) - rho(a,c,m) * rho(b,d,m) * Om_tmp(m) &
-                                    - rho(a,d,m) * rho(b,c,m) * Om_tmp(m)
-            end do
-
-            KC(ab,cd) = tmp_ab * KC(ab,cd)
+            KC(ab,cd) = -tmp_ab * (tmp(a,c,b,d) + tmp(a,d,b,c))
             if(c .eq. d) then
               KC(ab,cd) = 0.7071067811865475d0 * KC(ab,cd)
             endif
@@ -92,8 +96,87 @@ subroutine GW_ppBSE_static_kernel_C(ispin,eta,nBas,nC,nO,nV,nR,nS,nVV,lambda,ERI
     !$OMP END DO
     !$OMP END PARALLEL
 
-    deallocate(Om_tmp)
+    deallocate(tmp)
 
+
+!    do a=nO+1,nBas-nR
+!      do b=a,nBas-nR
+!        ab = ab + 1
+!        cd = 0
+!        do c=nO+1,nBas-nR
+!          do d=c,nBas-nR
+!            cd = cd + 1
+!
+!              chi = 0d0
+!              do m=1,nS
+!                eps = Om(m)**2 + eta**2
+!                chi = chi - rho(a,c,m)*rho(b,d,m)*Om(m)/eps &
+!                          - rho(a,d,m)*rho(b,c,m)*Om(m)/eps
+!              end do
+
+
+!    --- --- ---
+!    OpenMP implementation
+!    --- --- ---
+!
+!    a0 = nBas - nR - nO
+!    lambda4 = 4.d0 * lambda
+!    eta2 = eta * eta
+!
+!    allocate(Om_tmp(nS))
+!
+!    !$OMP PARALLEL DEFAULT(NONE) PRIVATE(m) SHARED(nS, eta2, Om, Om_tmp)
+!    !$OMP DO
+!    do m = 1, nS
+!      Om_tmp(m) = Om(m) / (Om(m)*Om(m) + eta2)
+!    enddo
+!    !$OMP END DO
+!    !$OMP END PARALLEL
+!
+!    !$OMP PARALLEL DEFAULT(NONE)                              &
+!    !$OMP          PRIVATE(a, b, aa, ab, c, d, cd, m, tmp_ab) &
+!    !$OMP          SHARED(nO, nBas, nR, nS, a0, lambda4, Om_tmp, rho, KC)
+!    !$OMP DO
+!    do a = nO+1, nBas-nR
+!      aa = a0 * (a - nO - 1) - (a - nO - 1) * (a - nO) / 2 - nO
+!      do b = a, nBas-nR
+!        ab = aa + b
+!
+!        tmp_ab = lambda4
+!        if(a .eq. b) then
+!          tmp_ab = 0.7071067811865475d0 * lambda4
+!        endif
+!
+!        cd = 0
+!        do c = nO+1, nBas-nR
+!          do d = c, nBas-nR
+!            cd = cd + 1
+!
+!            KC(ab,cd) = 0d0
+!            do m = 1, nS
+!              KC(ab,cd) = KC(ab,cd) - rho(a,c,m) * rho(b,d,m) * Om_tmp(m) &
+!                                    - rho(a,d,m) * rho(b,c,m) * Om_tmp(m)
+!            end do
+!
+!            KC(ab,cd) = tmp_ab * KC(ab,cd)
+!            if(c .eq. d) then
+!              KC(ab,cd) = 0.7071067811865475d0 * KC(ab,cd)
+!            endif
+!          enddo
+!        enddo
+!      enddo
+!    enddo
+!    !$OMP END DO
+!    !$OMP END PARALLEL
+!
+!    deallocate(Om_tmp)
+!    --- --- ---
+
+
+!    --- --- ---
+!    Naive implementation
+!    --- --- ---
+!
 !    ab = 0
 !    do a=nO+1,nBas-nR
 !      do b=a,nBas-nR
@@ -116,6 +199,7 @@ subroutine GW_ppBSE_static_kernel_C(ispin,eta,nBas,nC,nO,nV,nR,nS,nVV,lambda,ERI
 !        end do
 !      end do
 !    end do
+!    --- --- ---
 
   end if
 
@@ -129,19 +213,27 @@ subroutine GW_ppBSE_static_kernel_C(ispin,eta,nBas,nC,nO,nV,nR,nS,nVV,lambda,ERI
     lambda4 = 4.d0 * lambda
     eta2 = eta * eta
 
-    allocate(Om_tmp(nS))
+    allocate(tmp_m(nBas,nBas,nS))
+    allocate(tmp(nBas,nBas,nBas,nBas))
 
-    !$OMP PARALLEL DEFAULT(NONE) PRIVATE(m) SHARED(nS, eta2, Om, Om_tmp)
-    !$OMP DO
     do m = 1, nS
-      Om_tmp(m) = Om(m) / (Om(m)*Om(m) + eta2)
+      eps = Om(m) / (Om(m)*Om(m) + eta2)
+      do c = 1, nBas
+        do a = 1, nBas
+          tmp_m(a,c,m) = eps * rho(a,c,m)
+        enddo
+      enddo
     enddo
-    !$OMP END DO
-    !$OMP END PARALLEL
 
-    !$OMP PARALLEL DEFAULT(NONE)                      &
-    !$OMP          PRIVATE(a, b, aa, ab, c, d, cd, m) &
-    !$OMP          SHARED(nO, nBas, nR, nS, a0, lambda4, Om_tmp, rho, KC)
+    call dgemm("N", "T", nBas*nBas, nBas*nBas, nS, 1.d0,       &
+               tmp_m(1,1,1), nBas*nBas, rho(1,1,1), nBas*nBas, &
+               0.d0, tmp(1,1,1,1), nBas*nBas)
+
+    deallocate(tmp_m)
+
+    !$OMP PARALLEL DEFAULT(NONE)                   &
+    !$OMP          PRIVATE(a, b, aa, ab, c, d, cd) &
+    !$OMP          SHARED(nO, nBas, nR, nS, a0, lambda4, tmp, KC)
     !$OMP DO
     do a = nO+1, nBas-nR
       aa = a0 * (a - nO - 1) - (a - nO - 1) * (a - nO) / 2 - nO - 1
@@ -153,13 +245,7 @@ subroutine GW_ppBSE_static_kernel_C(ispin,eta,nBas,nC,nO,nV,nR,nS,nVV,lambda,ERI
           do d = c+1, nBas-nR
             cd = cd + 1
 
-            KC(ab,cd) = 0d0
-            do m = 1, nS
-              KC(ab,cd) = KC(ab,cd) - rho(a,c,m) * rho(b,d,m) * Om_tmp(m) &
-                                    + rho(a,d,m) * rho(b,c,m) * Om_tmp(m)
-            end do
-
-            KC(ab,cd) = lambda4 * KC(ab,cd)
+            KC(ab,cd) = lambda4 * (-tmp(a,c,b,d) + tmp(a,d,b,c))
           enddo
         enddo
       enddo
@@ -167,8 +253,63 @@ subroutine GW_ppBSE_static_kernel_C(ispin,eta,nBas,nC,nO,nV,nR,nS,nVV,lambda,ERI
     !$OMP END DO
     !$OMP END PARALLEL
 
-    deallocate(Om_tmp)
+    deallocate(tmp)
 
+
+!    --- --- ---
+!    OpenMP implementation
+!    --- --- ---
+!
+!    a0 = nBas - nR - nO - 1
+!    lambda4 = 4.d0 * lambda
+!    eta2 = eta * eta
+!
+!    allocate(Om_tmp(nS))
+!
+!    !$OMP PARALLEL DEFAULT(NONE) PRIVATE(m) SHARED(nS, eta2, Om, Om_tmp)
+!    !$OMP DO
+!    do m = 1, nS
+!      Om_tmp(m) = Om(m) / (Om(m)*Om(m) + eta2)
+!    enddo
+!    !$OMP END DO
+!    !$OMP END PARALLEL
+!
+!    !$OMP PARALLEL DEFAULT(NONE)                      &
+!    !$OMP          PRIVATE(a, b, aa, ab, c, d, cd, m) &
+!    !$OMP          SHARED(nO, nBas, nR, nS, a0, lambda4, Om_tmp, rho, KC)
+!    !$OMP DO
+!    do a = nO+1, nBas-nR
+!      aa = a0 * (a - nO - 1) - (a - nO - 1) * (a - nO) / 2 - nO - 1
+!      do b = a+1, nBas-nR
+!        ab = aa + b
+!
+!        cd = 0
+!        do c = nO+1, nBas-nR
+!          do d = c+1, nBas-nR
+!            cd = cd + 1
+!
+!            KC(ab,cd) = 0d0
+!            do m = 1, nS
+!              KC(ab,cd) = KC(ab,cd) - rho(a,c,m) * rho(b,d,m) * Om_tmp(m) &
+!                                    + rho(a,d,m) * rho(b,c,m) * Om_tmp(m)
+!            end do
+!
+!            KC(ab,cd) = lambda4 * KC(ab,cd)
+!          enddo
+!        enddo
+!      enddo
+!    enddo
+!    !$OMP END DO
+!    !$OMP END PARALLEL
+!
+!    deallocate(Om_tmp)
+!    --- --- ---
+
+
+!    --- --- ---
+!    Naive implementation
+!    --- --- ---
+!
 !    ab = 0
 !    do a=nO+1,nBas-nR
 !      do b=a+1,nBas-nR
@@ -191,6 +332,7 @@ subroutine GW_ppBSE_static_kernel_C(ispin,eta,nBas,nC,nO,nV,nR,nS,nVV,lambda,ERI
 !        end do
 !      end do
 !    end do
+!    --- --- ---
 
   end if