diff --git a/src/ML-UF3/uf3_bspline_basis2.cpp b/src/ML-UF3/uf3_bspline_basis2.cpp
index 7c16ab79d0..bb73e07970 100644
--- a/src/ML-UF3/uf3_bspline_basis2.cpp
+++ b/src/ML-UF3/uf3_bspline_basis2.cpp
@@ -36,9 +36,12 @@ uf3_bspline_basis2::uf3_bspline_basis2(LAMMPS *ulmp, const double *knots, double
        (square(knots[0]) - knots[0] * knots[1] - knots[0] * knots[2] + knots[1] * knots[2]));
   c2 = coefficient *
       (1.0 / (square(knots[0]) - knots[0] * knots[1] - knots[0] * knots[2] + knots[1] * knots[2]));
-  constants.push_back(c0);
-  constants.push_back(c1);
-  constants.push_back(c2);
+  //constants.push_back(c0);
+  //constants.push_back(c1);
+  //constants.push_back(c2);
+  constants[0] = c0;
+  constants[1] = c1;
+  constants[2] = c2;
   c0 = coefficient *
       (-knots[1] * knots[3] /
            (square(knots[1]) - knots[1] * knots[2] - knots[1] * knots[3] + knots[2] * knots[3]) -
@@ -56,9 +59,12 @@ uf3_bspline_basis2::uf3_bspline_basis2(LAMMPS *ulmp, const double *knots, double
   c2 = coefficient *
       (-1.0 / (square(knots[1]) - knots[1] * knots[2] - knots[1] * knots[3] + knots[2] * knots[3]) -
        1.0 / (knots[0] * knots[1] - knots[0] * knots[2] - knots[1] * knots[2] + square(knots[2])));
-  constants.push_back(c0);
-  constants.push_back(c1);
-  constants.push_back(c2);
+  //constants.push_back(c0);
+  //constants.push_back(c1);
+  //constants.push_back(c2);
+  constants[3] = c0;
+  constants[4] = c1;
+  constants[5] = c2;
   c0 = coefficient *
       (square(knots[3]) /
        (knots[1] * knots[2] - knots[1] * knots[3] - knots[2] * knots[3] + square(knots[3])));
@@ -67,9 +73,12 @@ uf3_bspline_basis2::uf3_bspline_basis2(LAMMPS *ulmp, const double *knots, double
        (knots[1] * knots[2] - knots[1] * knots[3] - knots[2] * knots[3] + square(knots[3])));
   c2 = coefficient *
       (1.0 / (knots[1] * knots[2] - knots[1] * knots[3] - knots[2] * knots[3] + square(knots[3])));
-  constants.push_back(c0);
-  constants.push_back(c1);
-  constants.push_back(c2);
+  //constants.push_back(c0);
+  //constants.push_back(c1);
+  //constants.push_back(c2);
+  constants[6] = c0;
+  constants[7] = c1;
+  constants[8] = c2;
 }
 
 uf3_bspline_basis2::~uf3_bspline_basis2() {}
@@ -96,7 +105,7 @@ double uf3_bspline_basis2::memory_usage()
 {
   double bytes = 0;
 
-  bytes += (double)constants.size()*sizeof(double);
+  bytes += (double)9*sizeof(double);
 
   return bytes;
 }
diff --git a/src/ML-UF3/uf3_bspline_basis2.h b/src/ML-UF3/uf3_bspline_basis2.h
index 90c6166f8c..b577e0c92a 100644
--- a/src/ML-UF3/uf3_bspline_basis2.h
+++ b/src/ML-UF3/uf3_bspline_basis2.h
@@ -28,7 +28,8 @@ class uf3_bspline_basis2 {
  public:
   uf3_bspline_basis2(LAMMPS *ulmp, const double *knots, double coefficient);
   ~uf3_bspline_basis2();
-  std::vector<double> constants;
+  //std::vector<double> constants;
+  double constants[9] = {};
   double eval0(double, double);
   double eval1(double, double);
   double eval2(double, double);
diff --git a/src/ML-UF3/uf3_bspline_basis3.cpp b/src/ML-UF3/uf3_bspline_basis3.cpp
index 3ed256777b..b2c7aa2acb 100644
--- a/src/ML-UF3/uf3_bspline_basis3.cpp
+++ b/src/ML-UF3/uf3_bspline_basis3.cpp
@@ -53,10 +53,14 @@ uf3_bspline_basis3::uf3_bspline_basis3(LAMMPS *ulmp, const double *knots, double
         square(knots[0]) * knots[3] - knots[0] * knots[1] * knots[2] -
         knots[0] * knots[1] * knots[3] - knots[0] * knots[2] * knots[3] +
         knots[1] * knots[2] * knots[3]));
-  constants.push_back(c0);
-  constants.push_back(c1);
-  constants.push_back(c2);
-  constants.push_back(c3);
+  //constants.push_back(c0);
+  //constants.push_back(c1);
+  //constants.push_back(c2);
+  //constants.push_back(c3);
+  constants[0] = c0;
+  constants[1] = c1;
+  constants[2] = c2;
+  constants[3] = c3;
   c0 = coefficient *
       (square(knots[1]) * knots[4] /
            (-cube(knots[1]) + square(knots[1]) * knots[2] + square(knots[1]) * knots[3] +
@@ -161,10 +165,14 @@ uf3_bspline_basis3::uf3_bspline_basis3(LAMMPS *ulmp, const double *knots, double
             knots[0] * knots[1] * knots[3] - knots[0] * knots[2] * knots[3] +
             square(knots[1]) * knots[3] - knots[1] * knots[2] * knots[3] -
             knots[1] * square(knots[3]) + knots[2] * square(knots[3])));
-  constants.push_back(c0);
-  constants.push_back(c1);
-  constants.push_back(c2);
-  constants.push_back(c3);
+  //constants.push_back(c0);
+  //constants.push_back(c1);
+  //constants.push_back(c2);
+  //constants.push_back(c3);
+  constants[4] = c0;
+  constants[5] = c1;
+  constants[6] = c2;
+  constants[7] = c3;
   c0 = coefficient *
       (-knots[0] * square(knots[3]) /
            (-knots[0] * knots[1] * knots[2] + knots[0] * knots[1] * knots[3] +
@@ -269,10 +277,14 @@ uf3_bspline_basis3::uf3_bspline_basis3(LAMMPS *ulmp, const double *knots, double
             knots[1] * knots[2] * knots[4] - knots[1] * knots[3] * knots[4] +
             square(knots[2]) * knots[4] - knots[2] * knots[3] * knots[4] -
             knots[2] * square(knots[4]) + knots[3] * square(knots[4])));
-  constants.push_back(c0);
-  constants.push_back(c1);
-  constants.push_back(c2);
-  constants.push_back(c3);
+  //constants.push_back(c0);
+  //constants.push_back(c1);
+  //constants.push_back(c2);
+  //constants.push_back(c3);
+  constants[8] = c0;
+  constants[9] = c1;
+  constants[10] = c2;
+  constants[11] = c3;
   c0 = coefficient *
       (cube(knots[4]) /
        (-knots[1] * knots[2] * knots[3] + knots[1] * knots[2] * knots[4] +
@@ -297,10 +309,14 @@ uf3_bspline_basis3::uf3_bspline_basis3(LAMMPS *ulmp, const double *knots, double
         knots[1] * knots[3] * knots[4] - knots[1] * square(knots[4]) +
         knots[2] * knots[3] * knots[4] - knots[2] * square(knots[4]) - knots[3] * square(knots[4]) +
         cube(knots[4])));
-  constants.push_back(c0);
-  constants.push_back(c1);
-  constants.push_back(c2);
-  constants.push_back(c3);
+  //constants.push_back(c0);
+  //constants.push_back(c1);
+  //constants.push_back(c2);
+  //constants.push_back(c3);
+  constants[12] = c0;
+  constants[13] = c1;
+  constants[14] = c2;
+  constants[15] = c3;
 }
 
 uf3_bspline_basis3::~uf3_bspline_basis3() {}
@@ -333,7 +349,7 @@ double uf3_bspline_basis3::memory_usage()
 {
   double bytes = 0;
 
-  bytes += (double)constants.size()*sizeof(double);
+  bytes += (double)16*sizeof(double);
 
   return bytes;
 }
diff --git a/src/ML-UF3/uf3_bspline_basis3.h b/src/ML-UF3/uf3_bspline_basis3.h
index 099a2302c7..70e1bbd2aa 100644
--- a/src/ML-UF3/uf3_bspline_basis3.h
+++ b/src/ML-UF3/uf3_bspline_basis3.h
@@ -29,7 +29,7 @@ class uf3_bspline_basis3 {
  public:
   uf3_bspline_basis3(LAMMPS *ulmp, const double *knots, double coefficient);
   ~uf3_bspline_basis3();
-  std::vector<double> constants;
+  double constants[16] = {};
   double eval0(double, double, double);
   double eval1(double, double, double);
   double eval2(double, double, double);