diff --git a/src/FermiCG.jl b/src/FermiCG.jl
index 736ed61..7f3046c 100644
--- a/src/FermiCG.jl
+++ b/src/FermiCG.jl
@@ -72,6 +72,7 @@ include("tucker_form_sigma_block_expand.jl")
 include("tucker_outer.jl")
 include("tucker_pt.jl")
 include("bst.jl")
+include("bst_helpers.jl")
 
 include("tpsci_inner.jl")
 include("tpsci_matvec_thread.jl")
diff --git a/src/bst_helpers.jl b/src/bst_helpers.jl
new file mode 100644
index 0000000..5115be0
--- /dev/null
+++ b/src/bst_helpers.jl
@@ -0,0 +1,43 @@
+
+
+"""
+    function bst_single_excitonic_basis(clusters, fspace::FockConfig{N}; R=1, Nk=2, T=Float64) where {N}
+"""
+function bst_single_excitonic_basis(clusters, fspace::FockConfig{N}, cluster_bases::Vector{ClusterBasis{A, T}}; R=1,number_of_single_excitations=4) where {N, T, A}
+    max_index = length(fspace.config)
+    ci_vector = BSTstate(clusters, fspace, cluster_bases, R=R)
+    dims = ones(Int, max_index)
+    configs = []
+    for i in 2:number_of_single_excitations
+        for indices in combinations(1:max_index, 1)
+            config = [in(k, indices) ? (i:i) : (1:1) for k in 1:max_index]
+            push!(configs, tuple(config...))
+        end
+    end
+    for config in configs
+        ci_vector[FermiCG.FockConfig(init_fspace)][FermiCG.TuckerConfig(config)] =
+            FermiCG.Tucker(tuple([zeros(Float64, dims...) for _ in 1:R]...))
+    end
+    return ci_vector
+end
+"""
+        function bst_biexcitonic_basis(clusters, fspace::FockConfig{N}; R=1, Nk=2, T=Float64) where {N}
+"""
+function bst_biexcitonic_basis(clusters, fspace::FockConfig{N}, cluster_bases::Vector{ClusterBasis{A, T}}; R=1) where {N, T, A}
+    max_index = length(fspace.config)
+    ci_vector = BSTstate(clusters, fspace, cluster_bases, R=R)
+    configs = []
+    for indices in combinations(1:max_index, 2)
+        config = [in(k, indices) ? (2:2) : (1:1) for k in 1:max_index]
+        push!(configs, tuple(config...))
+    end
+    dims = ones(Int, max_index)
+    for config in configs
+        ci_vector[FermiCG.FockConfig(init_fspace)][FermiCG.TuckerConfig(config)] =
+            FermiCG.Tucker(tuple([zeros(Float64, dims...) for _ in 1:R]...))
+    end
+
+    return ci_vector
+end
+
+