diff --git a/my_pyscf/lassi/lassis.py b/my_pyscf/lassi/lassis.py
index 32f084c1..b5aae0a0 100644
--- a/my_pyscf/lassi/lassis.py
+++ b/my_pyscf/lassi/lassis.py
@@ -12,7 +12,7 @@
 from mrh.my_pyscf.mcscf.productstate import ProductStateFCISolver
 from mrh.my_pyscf.lassi.excitations import ExcitationPSFCISolver
 from mrh.my_pyscf.lassi.spaces import spin_shuffle, spin_shuffle_ci
-from mrh.my_pyscf.lassi.spaces import _spin_shuffle, _spin_shuffle_ci_
+from mrh.my_pyscf.lassi.spaces import _spin_shuffle
 from mrh.my_pyscf.lassi.spaces import all_single_excitations, SingleLASRootspace
 from mrh.my_pyscf.lassi.spaces import orthogonal_excitations, combine_orthogonal_excitations
 from mrh.my_pyscf.lassi.lassi import LASSI
@@ -141,6 +141,7 @@ def single_excitations_ci (lsi, las2, las1, ncharge=1, sa_heff=True, deactivate_
         ciref = [[] for j in range (nfrags)]
         for k in range (nfrags):
             for space in psref: ciref[k].append (space.ci[k])
+        spaces[i].set_entmap_(psref[0])
         psref = [space.get_product_state_solver () for space in psref]
         psexc = ExcitationPSFCISolver (psref, ciref, las2.ncas_sub, las2.nelecas_sub,
                                        stdout=mol.stdout, verbose=mol.verbose,
@@ -302,6 +303,56 @@ def _spin_flip_products (spaces, spin_flips, nroots_ref=1, frozen_frags=None):
     spaces = [space for space in spaces if not ((space in seen) or seen.add (space))]
     return spaces
 
+def _spin_shuffle_ci_(spaces, spin_flips, nroots_ref, nroots_refc):
+    '''Memory-efficient version of the function spaces._spin_shuffle_ci_.
+    Based on the fact that we know there has only been one independent set
+    of vectors per fragment Hilbert space and that all possible individual
+    fragment spins must be accounted for already, so we are just recombining
+    them.'''
+    old_idx = []
+    new_idx = []
+    nfrag = spaces[0].nfrag
+    for ix, space in enumerate (spaces):
+        if space.has_ci ():
+            old_idx.append (ix)
+        else:
+            assert (ix >= nroots_refc)
+            new_idx.append (ix)
+            space.ci = [None for ifrag in range (space.nfrag)]
+    # Prepare charge-hop szrots
+    spaces_1c = spaces[nroots_ref:nroots_refc]
+    spaces_1c = [space for space in spaces_1c if len (space.entmap)==1]
+    ci_szrot_1c = []
+    for ix, space in enumerate (spaces_1c):
+        ifrag, jfrag = space.entmap[0] # must be a tuple of length 2
+        ci_szrot_1c.append (space.get_ci_szrot (ifrags=(ifrag,jfrag)))
+    charges0 = spaces[0].charges
+    for ix in new_idx:
+        idx = spaces[ix].excited_fragments (spaces[0])
+        space = spaces[ix]
+        for ifrag in np.where (~idx)[0]:
+            space.ci[ifrag] = spaces[0].ci[ifrag]
+        for ifrag in np.where (idx)[0]:
+            if space.charges[ifrag] != charges0[ifrag]: continue
+            sf = spin_flips[ifrag]
+            iflp = sf.smults == space.smults[ifrag]
+            iflp &= sf.spins == space.spins[ifrag]
+            assert (np.count_nonzero (iflp) == 1)
+            iflp = np.where (iflp)[0][0]
+            space.ci[ifrag] = sf.ci[iflp]
+        for (ci_i, ci_j), sp_1c in zip (ci_szrot_1c, spaces_1c):
+            ijfrag = sp_1c.entmap[0]
+            if ijfrag not in spaces[ix].entmap: continue
+            if np.any (sp_1c.charges[list(ijfrag)] != space.charges[list(ijfrag)]): continue
+            if np.any (sp_1c.smults[list(ijfrag)] != space.smults[list(ijfrag)]): continue
+            ifrag, jfrag = ijfrag
+            assert (space.ci[ifrag] is None)
+            assert (space.ci[jfrag] is None)
+            space.ci[ifrag] = ci_i[space.spins[ifrag]]
+            space.ci[jfrag] = ci_j[space.spins[jfrag]]
+        assert (space.has_ci ())
+    return spaces
+
 def spin_flip_products (las, spaces, spin_flips, nroots_ref=1):
     '''Inject spin-flips into las2 in all possible ways'''
     log = logger.new_logger (las, las.verbose)
@@ -309,7 +360,7 @@ def spin_flip_products (las, spaces, spin_flips, nroots_ref=1):
     spaces = _spin_flip_products (spaces, spin_flips, nroots_ref=nroots_ref)
     nfrags = spaces[0].nfrag
     spaces = _spin_shuffle (spaces)
-    spaces = _spin_shuffle_ci_(spaces)
+    spaces = _spin_shuffle_ci_(spaces, spin_flips, nroots_ref, las2_nroots)
     log.info ("LASSIS spin-excitation spaces: %d-%d", las2_nroots, len (spaces)-1)
     for i, space in enumerate (spaces[las2_nroots:]):
         if np.any (space.nelec != spaces[0].nelec):
@@ -326,8 +377,6 @@ def charge_excitation_products (lsi, spaces, las1):
     nfrags = lsi.nfrags
     space0 = spaces[0]
     i0, j0 = i, j = las1.nroots, len (spaces)
-    for space1 in spaces[i:j]:
-        space1.set_entmap_(space0)
     for product_order in range (2, (nfrags//2)+1):
         seen = set ()
         for i_list in itertools.combinations (range (i,j), product_order):
diff --git a/my_pyscf/lassi/spaces.py b/my_pyscf/lassi/spaces.py
index aaef2810..7915a2a1 100644
--- a/my_pyscf/lassi/spaces.py
+++ b/my_pyscf/lassi/spaces.py
@@ -170,10 +170,14 @@ def has_ci (self):
         if self.ci is None: return False
         return all ([c is not None for c in self.ci])
 
-    def get_ci_szrot (self):
+    def get_ci_szrot (self, ifrags=None):
         '''Generate the sets of CI vectors in which each vector for each fragment
         has the sz axis rotated in all possible ways.
 
+        Kwargs:
+            ifrags: list of integers
+                Optionally restrict ci_sz to particular fragments identified by ifrags
+
         Returns:
             ci_sz: list of dict of type {integer: ndarray}
                 dict keys are integerified "spin" quantum numbers; i.e., neleca-nelecb.
@@ -181,7 +185,8 @@ def get_ci_szrot (self):
         '''
         ci_sz = []
         ndet = self.get_ndet ()
-        for ifrag in range (self.nfrag):
+        if ifrags is None: ifrags = range (self.nfrag)
+        for ifrag in ifrags:
             norb, sz, ci = self.nlas[ifrag], self.spins[ifrag], self.ci[ifrag]
             ndeta, ndetb = ndet[ifrag]
             nelec = self.neleca[ifrag], self.nelecb[ifrag]