core: use center 0 mps for csf coefficients

pyblock2/driver/block2main

@@ -4496,6 +4496,9 @@ if not pre_run:
         dtrie = DeterminantTRIE(n_sites, True)
         mps.info.load_mutable()
         mps.load_mutable()
+        if mps.center != 0:
+            _print("Warning: sample an MPS with center != 0 will be highly inefficient!")
+            _print("One can load the MPS and do one extra sweep to change the center.")
         dtrie.evaluate(UnfusedMPS(mps), sample_cutoff, max_rank, VectorUInt8(sample_ref))
 
         if "sample_phase" in dic:

pyblock2/driver/core.py

@@ -3600,6 +3600,12 @@ def get_csf_coefficients(self, ket, cutoff=0.1, max_print=200, iprint=1):
         iprint = iprint >= 1 and (self.mpi is None or self.mpi.rank == self.mpi.root)
         import numpy as np, time
 
+        if ket.center != 0:
+            ket = self.copy_mps(ket, tag="CSF-TMP")
+            self.align_mps_center(ket, ref=0)
+            if iprint:
+                print("mps center changed (temporarily)")
+
         tx = time.perf_counter()
         dtrie = bw.bs.DeterminantTRIE(ket.n_sites, True)
         dtrie.evaluate(bw.bs.UnfusedMPS(ket), cutoff)
@@ -3638,9 +3644,10 @@ def get_csf_coefficients(self, ket, cutoff=0.1, max_print=200, iprint=1):
     def align_mps_center(self, ket, ref):
         if self.mpi is not None:
             self.mpi.barrier()
+        refc = ref if isinstance(ref, int) else ref.center
         ket.info.bond_dim = max(ket.info.bond_dim, ket.info.get_max_bond_dimension())
-        if ket.center != ref.center:
-            if ref.center == 0:
+        if ket.center != refc:
+            if refc == 0:
                 if ket.dot == 2:
                     ket.center += 1
                     if ket.canonical_form[-1] == 'C':

src/dmrg/determinant.hpp

@@ -42,7 +42,7 @@ namespace block2 {
 // time complexity: (D = MPS bond dimension)
 //    (n_dets << 4^n_sites) : n_sites * n_dets * D * D
 //    (n_dets  ~ 4^n_sites) : (4 / 3) * n_dets * D * D
-template <typename D, typename FL, uint8_t L = 4, typename IT = long long>
+template <typename D, typename FL, uint8_t L = 4, typename IT = uint32_t>
 struct TRIE {
     typedef typename GMatrix<FL>::FP FP;
     typedef IT XIT;
@@ -112,7 +112,7 @@ struct TRIE {
     }
     // find the index of a determinant
     // dets must be sorted
-    IT find(const vector<uint8_t> &det) {
+    int find(const vector<uint8_t> &det) {
         assert((int)det.size() == n_sites);
         IT cur = 0;
         for (int i = 0; i < n_sites; i++) {