diff --git a/ho_basis.jl b/ho_basis.jl
index b77939e..82d8238 100644
--- a/ho_basis.jl
+++ b/ho_basis.jl
@@ -1,3 +1,4 @@
+using SparseArrays
 using NuclearToolkit
 using SpecialFunctions
 include("helper.jl")
@@ -56,7 +57,7 @@ end
 get_V_matrix(V_l, ls, ns) = throw("unimplemented")
 
 function sp_T_matrix(ns, ls; ω=1.0, μ=1.0)
-    mat = zeros(length(ns), length(ns))
+    mat = spzeros(length(ns), length(ns))
     for idx in CartesianIndices(mat)
         (i, j) = Tuple(idx)
         if ls[i] == ls[j]
@@ -85,7 +86,7 @@ function Moshinsky_transform(Es, n1s, l1s, n2s, l2s, Λ)
     dcgm0 = NuclearToolkit.prep_dcgm0(l_max);
     d6j = NuclearToolkit.prep_d6j_int(E_max, j_max, to);
         
-    mat = zeros(length(Es), length(Es))
+    mat = spzeros(length(Es), length(Es))
     s = hcat(Es, n1s, l1s, n2s, l2s)
     for idx in CartesianIndices(mat)
         (i, j) = Tuple(idx)