diff --git a/my_pyscf/lassi/op_o1.py b/my_pyscf/lassi/op_o1.py
index 3604df01..85d77239 100644
--- a/my_pyscf/lassi/op_o1.py
+++ b/my_pyscf/lassi/op_o1.py
@@ -933,6 +933,16 @@ def _get_addr_range (self, raddr, *inv):
         return addr0 + np.dot (strides_inv, envaddr_inv)
 
     def _prepare_spec_addr_ovlp_(self, rbra, rket, *inv):
+        '''Prepare the cache for _get_spec_addr_ovlp.
+
+        Args:
+            rbra: integer
+                Index of bra rootspace for which to prepare the current cache.
+            rket: integer
+                Index of ket rootspace for which to prepare the current cache.
+            *inv: integers
+                Indices of nonspectator fragments
+        '''
         key = tuple ((rbra,rket)) + inv
         braket_table = self.nonuniq_exc[key]
         self._spec_addr_ovlp_cache = []
@@ -941,30 +951,12 @@ def _prepare_spec_addr_ovlp_(self, rbra, rket, *inv):
             self._spec_addr_ovlp_cache.append ((rbra1, rket1, b, k, o))
         return
 
-    def _get_cached_spec_addr_ovlp (self, bra, ket, *inv):
-        rbra, rket = self.rootaddr[bra], self.rootaddr[ket]
-        braenv = self.envaddr[bra]
-        ketenv = self.envaddr[ket]
-        key = tuple ((rbra,rket)) + inv
-        braket_table = self.nonuniq_exc[key]
-        bra_rng = []
-        ket_rng = []
-        facs = []
-        for (rbra1, rket1, b, k, o) in self._spec_addr_ovlp_cache:
-            dbra = np.dot (braenv, self.strides[rbra1])
-            dket = np.dot (ketenv, self.strides[rket1])
-            bra_rng.append (b+dbra)
-            ket_rng.append (k+dket)
-            facs.append (o)
-        bra_rng = np.concatenate (bra_rng)
-        ket_rng = np.concatenate (ket_rng)
-        facs = np.concatenate (facs)
-        return bra_rng, ket_rng, facs
-
     def _get_spec_addr_ovlp (self, bra, ket, *inv):
         '''Obtain the integer indices and overlap*permutation factors for all pairs of model states
         for which a specified list of nonspectator fragments are in same state that they are in a
-        provided input pair bra, ket.
+        provided input pair bra, ket. Uses a cache that must be prepared beforehand by the function
+        _prepare_spec_addr_ovlp_(rbra, rket, *inv), where rbra and rket must be the rootspace
+        indices corresponding to this function's bra, ket arguments.
 
         Args:
             bra: integer
@@ -991,10 +983,9 @@ def _get_spec_addr_ovlp (self, bra, ket, *inv):
         bra_rng = []
         ket_rng = []
         facs = []
-        for rbra1, rket1 in braket_table:
+        for (rbra1, rket1, b, k, o) in self._spec_addr_ovlp_cache:
             dbra = np.dot (braenv, self.strides[rbra1])
             dket = np.dot (ketenv, self.strides[rket1])
-            b, k, o = self._get_spec_addr_ovlp_1space (rbra1, rket1, *inv)
             bra_rng.append (b+dbra)
             ket_rng.append (k+dket)
             facs.append (o)
@@ -1060,14 +1051,14 @@ def _get_D2_(self, bra, ket):
         return self.d2
 
     def _put_D1_(self, bra, ket, D1, *inv):
-        bra1, ket1, wgt = self._get_cached_spec_addr_ovlp (bra, ket, *inv)
+        bra1, ket1, wgt = self._get_spec_addr_ovlp (bra, ket, *inv)
         self._put_SD1_(bra1, ket1, D1, wgt)
 
     def _put_SD1_(self, bra, ket, D1, wgt):
         self.tdm1s[bra,ket,:] += np.multiply.outer (wgt, D1)
 
     def _put_D2_(self, bra, ket, D2, *inv):
-        bra1, ket1, wgt = self._get_cached_spec_addr_ovlp (bra, ket, *inv)
+        bra1, ket1, wgt = self._get_spec_addr_ovlp (bra, ket, *inv)
         self._put_SD2_(bra1, ket1, D2, wgt)
 
     def _put_SD2_(self, bra, ket, D2, wgt):
@@ -1404,7 +1395,7 @@ def _put_D1_(self, bra, ket, D1, *inv):
         D1 = D1.sum (0)
         #self.s2[bra,ket] += (np.trace (M1)/2)**2 + np.trace (D1)/2
         s2 = 3*np.trace (D1)/4
-        bra1, ket1, wgt = self._get_cached_spec_addr_ovlp (bra, ket, *inv)
+        bra1, ket1, wgt = self._get_spec_addr_ovlp (bra, ket, *inv)
         self._put_ham_s2_(bra1, ket1, ham, s2, wgt)
 
     def _put_ham_s2_(self, bra, ket, ham, s2, wgt):
@@ -1416,7 +1407,7 @@ def _put_D2_(self, bra, ket, D2, *inv):
         M2 = np.einsum ('sppqq->s', D2) / 4
         s2 = M2[0] + M2[3] - M2[1] - M2[2]
         s2 -= np.einsum ('pqqp->', D2[1] + D2[2]) / 2
-        bra1, ket1, wgt = self._get_cached_spec_addr_ovlp (bra, ket, *inv)
+        bra1, ket1, wgt = self._get_spec_addr_ovlp (bra, ket, *inv)
         self._put_ham_s2_(bra1, ket1, ham, s2, wgt)
 
     def _add_transpose_(self):
@@ -1639,7 +1630,7 @@ def _get_vecs_(self, bra, ket):
         return hci_f_ab, excfrags
 
     def _put_vecs_(self, bra, ket, vecs, *inv):
-        bras, kets, facs = self._get_cached_spec_addr_ovlp (bra, ket, *inv)
+        bras, kets, facs = self._get_spec_addr_ovlp (bra, ket, *inv)
         for bra, ket, fac in zip (bras, kets, facs):
             self._put_Svecs_(bra, ket, [fac*vec for vec in vecs])