diff --git a/.gitignore b/.gitignore
index 83de1e85..24d79df6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,3 +11,5 @@ docs/src/generated/
 
 # data too large for github
 examples/aHfO2/
+*.xyz
+*.csv
diff --git a/src/Kernels/kernels.jl b/src/Kernels/kernels.jl
index 681ff269..c7414aa9 100644
--- a/src/Kernels/kernels.jl
+++ b/src/Kernels/kernels.jl
@@ -89,7 +89,7 @@ function KernelMatrix(
     n = length(F)
     K = zeros(n, n)
     for i = 1:n
-        for j = 1:n
+        for j = i:n
             K[i, j] = compute_kernel(F[i], F[j], k)
         end
     end