diff --git a/my_pyscf/lassi/excitations.py b/my_pyscf/lassi/excitations.py
index 47654f10..70ff66a3 100644
--- a/my_pyscf/lassi/excitations.py
+++ b/my_pyscf/lassi/excitations.py
@@ -12,6 +12,8 @@
 from pyscf.lib import temporary_env
 op = (op_o0, op_o1)
 
+LOWEST_REFOVLP_EIGVAL_THRESH = getattr (__config__, 'lassi_excitations_refovlp_eigval_thresh', 1e-8)
+
 def only_ground_states (ci0):
     '''For a list of sequences of CI vectors in the same Hilbert space,
     generate a list in which all but the first element of each sequence
@@ -24,7 +26,7 @@ def only_ground_states (ci0):
         ci1.append (c)
     return ci1
 
-def lowest_refovlp_eigval (ham_pq, ovlp_thresh=1e-8):
+def lowest_refovlp_eigval (ham_pq, ovlp_thresh=LOWEST_REFOVLP_EIGVAL_THRESH):
     ''' Return the lowest eigenvalue of the matrix ham_pq, whose corresponding
     eigenvector has nonzero overlap with the first basis function. '''
     e_all, u_all = linalg.eigh (ham_pq)