diff --git a/anphon/scph.cpp b/anphon/scph.cpp
index 0e214faa..c891b4eb 100644
--- a/anphon/scph.cpp
+++ b/anphon/scph.cpp
@@ -1081,7 +1081,7 @@ void Scph::compute_V4_elements_mpi_over_kpoint(std::complex<double> ***v4_out,
     maxsize=(maxsize<<31)-1;
 
     const size_t count = nk2_prod * ns4;
-    const size_t count_sub = nk2_prod * ns2;
+    const size_t count_sub = ns4;
 
     if (count <= maxsize) {
 #ifdef MPI_CXX_DOUBLE_COMPLEX
@@ -1091,21 +1091,36 @@ void Scph::compute_V4_elements_mpi_over_kpoint(std::complex<double> ***v4_out,
         MPI_Allreduce(&v4_mpi[0][0][0], &v4_out[0][0][0], count,
                       MPI_COMPLEX16, MPI_SUM, MPI_COMM_WORLD);
 #endif
-    } else {
-        for (is = 0; is < ns2; ++is) {
+    } else if (count_sub <= maxsize) {
+        for (size_t ik_prod = 0; ik_prod < nk2_prod; ++ik_prod) {
 #ifdef MPI_CXX_DOUBLE_COMPLEX
-            MPI_Allreduce(&v4_mpi[0][0][is], &v4_out[0][0][is], count_sub,
-        MPI_CXX_DOUBLE_COMPLEX, MPI_SUM, MPI_COMM_WORLD);
+            MPI_Allreduce(&v4_mpi[ik_prod][0][0], &v4_out[ik_prod][0][0],
+                          count_sub,
+                          MPI_CXX_DOUBLE_COMPLEX, MPI_SUM, MPI_COMM_WORLD);
 #else
-            MPI_Allreduce(&v4_mpi[0][0][is], &v4_out[0][0][is], count_sub,
+            MPI_Allreduce(&v4_mpi[ik_prod][0][0], &v4_out[ik_prod][0][0],
+                          count_sub,
                           MPI_COMPLEX16, MPI_SUM, MPI_COMM_WORLD);
 #endif
         }
+    } else {
+        for (size_t ik_prod = 0; ik_prod < nk2_prod; ++ik_prod) {
+            for (is = 0; is < ns2; ++is) {
+#ifdef MPI_CXX_DOUBLE_COMPLEX
+                MPI_Allreduce(&v4_mpi[ik_prod][is][0], &v4_out[ik_prod][is][0],
+                          ns2,
+                          MPI_CXX_DOUBLE_COMPLEX, MPI_SUM, MPI_COMM_WORLD);
+#else
+                MPI_Allreduce(&v4_mpi[ik_prod][is][0], &v4_out[ik_prod][is][0],
+                              ns2,
+                              MPI_COMPLEX16, MPI_SUM, MPI_COMM_WORLD);
+#endif
+            }
+        }
     }
 
     memory->deallocate(v4_mpi);
 
-
     zerofill_elements_acoustic_at_gamma(omega2_harmonic, v4_out, 4);
 
 
@@ -1318,7 +1333,7 @@ void Scph::compute_V4_elements_mpi_over_band(std::complex<double> ***v4_out,
     maxsize=(maxsize<<31)-1;
 
     const size_t count = nk2_prod * ns4;
-    const size_t count_sub = nk2_prod * ns2;
+    const size_t count_sub = ns4;
 
     if (count <= maxsize) {
 #ifdef MPI_CXX_DOUBLE_COMPLEX
@@ -1328,16 +1343,32 @@ void Scph::compute_V4_elements_mpi_over_band(std::complex<double> ***v4_out,
         MPI_Allreduce(&v4_mpi[0][0][0], &v4_out[0][0][0], count,
                       MPI_COMPLEX16, MPI_SUM, MPI_COMM_WORLD);
 #endif
-    } else {
-        for (is = 0; is < ns2; ++is) {
+    } else if (count_sub <= maxsize) {
+        for (size_t ik_prod = 0; ik_prod < nk2_prod; ++ik_prod) {
 #ifdef MPI_CXX_DOUBLE_COMPLEX
-            MPI_Allreduce(&v4_mpi[0][0][is], &v4_out[0][0][is], count_sub,
-        MPI_CXX_DOUBLE_COMPLEX, MPI_SUM, MPI_COMM_WORLD);
+            MPI_Allreduce(&v4_mpi[ik_prod][0][0], &v4_out[ik_prod][0][0],
+                          count_sub,
+                          MPI_CXX_DOUBLE_COMPLEX, MPI_SUM, MPI_COMM_WORLD);
 #else
-            MPI_Allreduce(&v4_mpi[0][0][is], &v4_out[0][0][is], count_sub,
+            MPI_Allreduce(&v4_mpi[ik_prod][0][0], &v4_out[ik_prod][0][0],
+                          count_sub,
                           MPI_COMPLEX16, MPI_SUM, MPI_COMM_WORLD);
 #endif
         }
+    } else {
+        for (size_t ik_prod = 0; ik_prod < nk2_prod; ++ik_prod) {
+            for (is = 0; is < ns2; ++is) {
+#ifdef MPI_CXX_DOUBLE_COMPLEX
+                MPI_Allreduce(&v4_mpi[ik_prod][is][0], &v4_out[ik_prod][is][0],
+                          ns2,
+                          MPI_CXX_DOUBLE_COMPLEX, MPI_SUM, MPI_COMM_WORLD);
+#else
+                MPI_Allreduce(&v4_mpi[ik_prod][is][0], &v4_out[ik_prod][is][0],
+                              ns2,
+                              MPI_COMPLEX16, MPI_SUM, MPI_COMM_WORLD);
+#endif
+            }
+        }
     }
 
     memory->deallocate(v4_mpi);