diff --git a/example/kbe_polyacetylene.py b/example/kbe_polyacetylene.py
index 77d9a37d..22f0f613 100644
--- a/example/kbe_polyacetylene.py
+++ b/example/kbe_polyacetylene.py
@@ -5,7 +5,7 @@
 import numpy as np
 from pyscf.pbc import df, gto, scf
 
-from quemb.kbe import BE, FragPart
+from quemb.kbe import BE, fragpart
 
 kpt = [1, 1, 3]
 cell = gto.Cell()
@@ -48,7 +48,7 @@
 kpoint_energy = kmf.kernel()
 
 # Define fragment in the supercell
-kfrag = FragPart(be_type="be2", mol=cell, kpt=kpt, frozen_core=True)
+kfrag = fragpart(be_type="be2", mol=cell, kpt=kpt, frozen_core=True)
 # Initialize BE
 mykbe = BE(kmf, kfrag, kpts=kpts)
 
diff --git a/example/molbe_dmrg_block2.py b/example/molbe_dmrg_block2.py
index e3e329ab..d1e99e32 100644
--- a/example/molbe_dmrg_block2.py
+++ b/example/molbe_dmrg_block2.py
@@ -6,7 +6,7 @@
 import numpy as np
 from pyscf import cc, fci, gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 from quemb.molbe.solver import DMRG_ArgsUser
 
 # We'll consider the dissociation curve for a 1D chain of 8 H-atoms:
@@ -42,7 +42,7 @@
     # any clear advantage to using any one scheme over another,
     # the Pipek-Mezey scheme continues to be the most popular. With
     # BE-DMRG, localization takes place prior to fragmentation:
-    fobj = FragPart(be_type="be1", mol=mol)
+    fobj = fragpart(be_type="be1", mol=mol)
     mybe = BE(
         mf,
         fobj,
@@ -88,7 +88,7 @@
 mol.charge = 0
 mol.spin = 0
 mol.build()
-fobj = FragPart(be_type="be2", mol=mol)
+fobj = fragpart(be_type="be2", mol=mol)
 mybe = BE(mf, fobj, lo_method="pipek-mezey", pop_method="lowdin")
 
 # We automatically construct the fragment DMRG schedules based on user keywords.
diff --git a/example/molbe_h8_chemical_potential.py b/example/molbe_h8_chemical_potential.py
index bbd871a9..456f8016 100644
--- a/example/molbe_h8_chemical_potential.py
+++ b/example/molbe_h8_chemical_potential.py
@@ -3,7 +3,7 @@
 
 from pyscf import fci, gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 # PySCF HF generated mol & mf (molecular desciption & HF object)
 mol = gto.M(
@@ -33,7 +33,7 @@
 # Perform BE calculations with different fragment schemes:
 
 # Define BE1 fragments
-fobj = FragPart(be_type="be1", mol=mol)
+fobj = fragpart(be_type="be1", mol=mol)
 # Initialize BE
 mybe = BE(mf, fobj)
 # Perform chemical potential optimization
@@ -45,7 +45,7 @@
 print(f"*** BE1 Correlation Energy Error (%) : {err_:>8.4f} %")
 
 # Define BE2 fragments
-fobj = FragPart(be_type="be2", mol=mol)
+fobj = fragpart(be_type="be2", mol=mol)
 mybe = BE(mf, fobj)
 mybe.optimize(solver="FCI", only_chem=True)
 
@@ -55,7 +55,7 @@
 print(f"*** BE2 Correlation Energy Error (%) : {err_:>8.4f} %")
 
 # Define BE3 fragments
-fobj = FragPart(be_type="be3", mol=mol)
+fobj = fragpart(be_type="be3", mol=mol)
 mybe = BE(mf, fobj)
 mybe.optimize(solver="FCI", only_chem=True)
 
diff --git a/example/molbe_h8_density_matching.py b/example/molbe_h8_density_matching.py
index 2a36f04b..a14414b7 100644
--- a/example/molbe_h8_density_matching.py
+++ b/example/molbe_h8_density_matching.py
@@ -3,7 +3,7 @@
 
 from pyscf import fci, gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 # PySCF HF generated mol & mf (molecular desciption & HF object)
 mol = gto.M(
@@ -33,7 +33,7 @@
 # Perform BE calculations with different fragment schemes:
 
 # Define BE2 fragments
-fobj = FragPart(be_type="be2", mol=mol)
+fobj = fragpart(be_type="be2", mol=mol)
 mybe = BE(mf, fobj)
 mybe.optimize(solver="FCI")
 
@@ -43,7 +43,7 @@
 print(f"*** BE2 Correlation Energy Error (%) : {err_:>8.4f} %")
 
 # Define BE3 fragments
-fobj = FragPart(be_type="be3", mol=mol)
+fobj = fragpart(be_type="be3", mol=mol)
 mybe = BE(mf, fobj)
 mybe.optimize(solver="FCI")
 
diff --git a/example/molbe_hexene_oneshot_uccsd.py b/example/molbe_hexene_oneshot_uccsd.py
index d31b2c99..e4118617 100644
--- a/example/molbe_hexene_oneshot_uccsd.py
+++ b/example/molbe_hexene_oneshot_uccsd.py
@@ -4,7 +4,7 @@
 
 from pyscf import gto, scf
 
-from quemb.molbe import UBE, FragPart
+from quemb.molbe import UBE, fragpart
 
 # Give path to structure xyz file
 structure = "data/hexene.xyz"
@@ -25,7 +25,7 @@
 nproc = 1
 
 # Initialize fragments without frozen core approximation at BE2 level
-fobj = FragPart(frag_type="autogen", be_type="be2", mol=mol, frozen_core=False)
+fobj = fragpart(frag_type="autogen", be_type="be2", mol=mol, frozen_core=False)
 # Initialize UBE
 mybe = UBE(mf, fobj)
 
diff --git a/example/molbe_io_fcidump.py b/example/molbe_io_fcidump.py
index 2133802a..fccef15c 100644
--- a/example/molbe_io_fcidump.py
+++ b/example/molbe_io_fcidump.py
@@ -1,7 +1,7 @@
 # Illustrates how fcidump file containing fragment hamiltonian
 # can be generated using be2fcidump
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 from quemb.molbe.misc import be2fcidump, libint2pyscf
 from quemb.shared.config import settings
 
@@ -15,7 +15,7 @@
 mf.kernel()
 
 # Construct fragments for BE
-fobj = FragPart(be_type="be2", mol=mol)
+fobj = fragpart(be_type="be2", mol=mol)
 oct_be = BE(mf, fobj)
 
 # Write out fcidump file for each fragment
diff --git a/example/molbe_octane.py b/example/molbe_octane.py
index d1779042..eef4cf5b 100644
--- a/example/molbe_octane.py
+++ b/example/molbe_octane.py
@@ -2,7 +2,7 @@
 
 from pyscf import cc, gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 # Perform pyscf HF calculation to get mol & mf objects
 mol = gto.M(
@@ -50,7 +50,7 @@
 print(f"*** CCSD Correlation Energy: {ccsd_ecorr:>14.8f} Ha", flush=True)
 
 # initialize fragments (use frozen core approximation)
-fobj = FragPart(be_type="be2", mol=mol, frozen_core=True)
+fobj = fragpart(be_type="be2", mol=mol, frozen_core=True)
 # Initialize BE
 mybe = BE(mf, fobj)
 
diff --git a/example/molbe_octane_get_rdms.py b/example/molbe_octane_get_rdms.py
index 9fd6e7bc..e1466c31 100644
--- a/example/molbe_octane_get_rdms.py
+++ b/example/molbe_octane_get_rdms.py
@@ -2,7 +2,7 @@
 
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 # Perform pyscf HF calculation to get mol & mf objects
 mol = gto.M(
@@ -44,7 +44,7 @@
 mf.kernel()
 
 # initialize fragments (use frozen core approximation)
-fobj = FragPart(be_type="be2", mol=mol, frozen_core=True)
+fobj = fragpart(be_type="be2", mol=mol, frozen_core=True)
 # Initialize BE
 mybe = BE(mf, fobj)
 
diff --git a/example/molbe_ppp.py b/example/molbe_ppp.py
index ac0bd71d..55251ee3 100644
--- a/example/molbe_ppp.py
+++ b/example/molbe_ppp.py
@@ -2,7 +2,7 @@
 
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 # Perform pyscf HF calculation to get mol & mf objects
 mol = gto.M(
@@ -32,7 +32,7 @@
 mf.kernel()
 
 # Define fragments; use IAO scheme with 'sto-3g' as the minimal basis set
-fobj = FragPart(be_type="be2", mol=mol, iao_valence_basis="sto-3g", frozen_core=True)
+fobj = fragpart(be_type="be2", mol=mol, iao_valence_basis="sto-3g", frozen_core=True)
 
 # Initialize BE
 mybe = BE(mf, fobj, lo_method="iao")
diff --git a/src/quemb/kbe/__init__.py b/src/quemb/kbe/__init__.py
index f925e103..e1e48e92 100644
--- a/src/quemb/kbe/__init__.py
+++ b/src/quemb/kbe/__init__.py
@@ -1,4 +1,4 @@
-from quemb.kbe.fragment import FragPart
+from quemb.kbe.fragment import fragpart
 from quemb.kbe.pbe import BE
 
-__all__ = ["FragPart", "BE"]
+__all__ = ["fragpart", "BE"]
diff --git a/src/quemb/kbe/fragment.py b/src/quemb/kbe/fragment.py
index 9b620477..b27d7e0a 100644
--- a/src/quemb/kbe/fragment.py
+++ b/src/quemb/kbe/fragment.py
@@ -7,7 +7,7 @@
 from quemb.shared.helper import copy_docstring
 
 
-class FragPart:
+class fragpart:
     def __init__(
         self,
         natom=0,
diff --git a/src/quemb/kbe/pbe.py b/src/quemb/kbe/pbe.py
index 23e31f2f..d08fed13 100644
--- a/src/quemb/kbe/pbe.py
+++ b/src/quemb/kbe/pbe.py
@@ -12,7 +12,7 @@
 from pyscf.pbc import df, gto
 from pyscf.pbc.df.df_jk import _ewald_exxdiv_for_G0
 
-from quemb.kbe.fragment import FragPart
+from quemb.kbe.fragment import fragpart
 from quemb.kbe.lo import Mixin_k_Localize
 from quemb.kbe.misc import print_energy, storePBE
 from quemb.kbe.pfrag import Frags
@@ -51,7 +51,7 @@ class BE(Mixin_k_Localize):
     def __init__(
         self,
         mf: pbc.scf.hf.SCF,
-        fobj: FragPart,
+        fobj: fragpart,
         eri_file: PathLike = "eri_file.h5",
         lo_method: str = "lowdin",
         compute_hf: bool = True,
diff --git a/src/quemb/molbe/__init__.py b/src/quemb/molbe/__init__.py
index 7da7c018..ffe6c654 100644
--- a/src/quemb/molbe/__init__.py
+++ b/src/quemb/molbe/__init__.py
@@ -1,5 +1,5 @@
-from quemb.molbe.fragment import FragPart
+from quemb.molbe.fragment import fragpart
 from quemb.molbe.mbe import BE
 from quemb.molbe.ube import UBE
 
-__all__ = ["FragPart", "BE", "UBE"]
+__all__ = ["fragpart", "BE", "UBE"]
diff --git a/src/quemb/molbe/fragment.py b/src/quemb/molbe/fragment.py
index 55b3bc43..c6b05c97 100644
--- a/src/quemb/molbe/fragment.py
+++ b/src/quemb/molbe/fragment.py
@@ -7,7 +7,7 @@
 from quemb.shared.helper import copy_docstring
 
 
-class FragPart:
+class fragpart:
     """Fragment/partitioning definition
 
     Interfaces two main fragmentation functions (autogen & chain) in MolBE. It defines
diff --git a/src/quemb/molbe/mbe.py b/src/quemb/molbe/mbe.py
index f4a19dda..520d3ba6 100644
--- a/src/quemb/molbe/mbe.py
+++ b/src/quemb/molbe/mbe.py
@@ -10,7 +10,7 @@
 
 from quemb.molbe.be_parallel import be_func_parallel
 from quemb.molbe.eri_onthefly import integral_direct_DF
-from quemb.molbe.fragment import FragPart
+from quemb.molbe.fragment import fragpart
 from quemb.molbe.lo import MixinLocalize
 from quemb.molbe.misc import print_energy_cumulant, print_energy_noncumulant
 from quemb.molbe.opt import BEOPT
@@ -67,7 +67,7 @@ class BE(MixinLocalize):
     def __init__(
         self,
         mf: scf.hf.SCF,
-        fobj: FragPart,
+        fobj: fragpart,
         eri_file: PathLike = "eri_file.h5",
         lo_method: str = "lowdin",
         pop_method: str | None = None,
diff --git a/src/quemb/molbe/misc.py b/src/quemb/molbe/misc.py
index 0617a2f0..aad0eefc 100644
--- a/src/quemb/molbe/misc.py
+++ b/src/quemb/molbe/misc.py
@@ -9,7 +9,7 @@
 from pyscf.lib import chkfile
 from pyscf.tools import fcidump
 
-from quemb.molbe.fragment import FragPart
+from quemb.molbe.fragment import fragpart
 
 
 def libint2pyscf(
@@ -438,7 +438,7 @@ def be2puffin(
 
     # Finished initial reference HF: now, fragmentation step
 
-    fobj = FragPart(
+    fobj = fragpart(
         be_type=be_type, frag_type="autogen", mol=mol, frozen_core=frozen_core
     )
     time_post_fragpart = time.time()
diff --git a/src/quemb/molbe/ube.py b/src/quemb/molbe/ube.py
index 893149c9..5fd3153b 100644
--- a/src/quemb/molbe/ube.py
+++ b/src/quemb/molbe/ube.py
@@ -20,7 +20,7 @@
 from pyscf.scf.uhf import UHF
 
 from quemb.molbe.be_parallel import be_func_parallel_u
-from quemb.molbe.fragment import FragPart
+from quemb.molbe.fragment import fragpart
 from quemb.molbe.mbe import BE
 from quemb.molbe.pfrag import Frags
 from quemb.molbe.solver import be_func_u
@@ -33,7 +33,7 @@ class UBE(BE):  # 🍠
     def __init__(
         self,
         mf: UHF,
-        fobj: FragPart,
+        fobj: fragpart,
         scratch_dir: WorkDir | None = None,
         eri_file: PathLike = "eri_file.h5",
         lo_method: PathLike = "lowdin",
diff --git a/tests/chem_dm_kBE_test.py b/tests/chem_dm_kBE_test.py
index 9a00741f..9f720de1 100644
--- a/tests/chem_dm_kBE_test.py
+++ b/tests/chem_dm_kBE_test.py
@@ -11,7 +11,7 @@
 from numpy import eye
 from pyscf.pbc import df, gto, scf
 
-from quemb.kbe import BE, FragPart
+from quemb.kbe import BE, fragpart
 
 try:
     import libdmet
@@ -98,7 +98,7 @@ def periodic_test(
         kmf.conv_tol = 1e-12
         kmf.kernel()
 
-        kfrag = FragPart(
+        kfrag = fragpart(
             be_type=be_type, mol=cell, frag_type=frag_type, kpt=kpt, frozen_core=True
         )
         mykbe = BE(kmf, kfrag, kpts=kpts)
diff --git a/tests/chempot_molBE_test.py b/tests/chempot_molBE_test.py
index 6a28fe94..79a1ba7c 100644
--- a/tests/chempot_molBE_test.py
+++ b/tests/chempot_molBE_test.py
@@ -10,7 +10,7 @@
 
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 
 class TestBE_restricted(unittest.TestCase):
@@ -52,7 +52,7 @@ def molecular_restricted_test(
     ):
         mf = scf.RHF(mol)
         mf.kernel()
-        fobj = FragPart(frag_type=frag_type, be_type=be_type, mol=mol)
+        fobj = fragpart(frag_type=frag_type, be_type=be_type, mol=mol)
         mybe = BE(mf, fobj)
         mybe.optimize(solver="CCSD", method="QN", only_chem=only_chem)
         self.assertAlmostEqual(
diff --git a/tests/dm_molBE_test.py b/tests/dm_molBE_test.py
index 6d81a51b..b5ee2e11 100644
--- a/tests/dm_molBE_test.py
+++ b/tests/dm_molBE_test.py
@@ -9,7 +9,7 @@
 
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 
 class TestBE_restricted(unittest.TestCase):
@@ -31,7 +31,7 @@ def molecular_QN_test(
         mf = scf.RHF(mol)
         mf.max_cycle = 100
         mf.kernel()
-        fobj = FragPart(frag_type=frag_type, be_type=be_type, mol=mol)
+        fobj = fragpart(frag_type=frag_type, be_type=be_type, mol=mol)
         mybe1 = BE(mf, fobj)
         mybe1.optimize(
             solver="CCSD", method="QN", trust_region=False, only_chem=only_chem
diff --git a/tests/dmrg_molBE_test.py b/tests/dmrg_molBE_test.py
index 351c4ca2..11020e32 100644
--- a/tests/dmrg_molBE_test.py
+++ b/tests/dmrg_molBE_test.py
@@ -9,7 +9,7 @@
 
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 try:
     from pyscf import dmrgscf
@@ -39,7 +39,7 @@ def molecular_DMRG_test(
         with tempfile.TemporaryDirectory() as tmp:
             mf = scf.RHF(mol)
             mf.kernel()
-            fobj = FragPart(frag_type=frag_type, be_type=be_type, mol=mol)
+            fobj = fragpart(frag_type=frag_type, be_type=be_type, mol=mol)
             mybe = BE(mf, fobj, lo_method="pipek", pop_method="lowdin")
             mybe.oneshot(
                 solver="block2",
diff --git a/tests/eri_onthefly_test.py b/tests/eri_onthefly_test.py
index 4dcb8623..5c09d25e 100644
--- a/tests/eri_onthefly_test.py
+++ b/tests/eri_onthefly_test.py
@@ -10,7 +10,7 @@
 
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 
 class TestDF_ontheflyERI(unittest.TestCase):
@@ -29,7 +29,7 @@ def test_octane_BE2(self):
         mf = scf.RHF(mol)
         mf.direct_scf = True
         mf.kernel()
-        fobj = FragPart(frag_type="autogen", be_type="be2", mol=mol)
+        fobj = fragpart(frag_type="autogen", be_type="be2", mol=mol)
         mybe = BE(mf, fobj, integral_direct_DF=True)
         self.assertAlmostEqual(
             mybe.ebe_hf,
diff --git a/tests/fragmentation_test.py b/tests/fragmentation_test.py
index f9056e77..a5f31962 100644
--- a/tests/fragmentation_test.py
+++ b/tests/fragmentation_test.py
@@ -9,7 +9,7 @@
 
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 
 class TestBE_Fragmentation(unittest.TestCase):
@@ -1377,7 +1377,7 @@ def run_energies_test(
     ):
         Es = {"target": target}
         for frag_type in ["autogen", "graphgen"]:
-            fobj = FragPart(frag_type=frag_type, be_type=be_type, mol=mf.mol)
+            fobj = fragpart(frag_type=frag_type, be_type=be_type, mol=mf.mol)
             mbe = BE(mf, fobj)
             mbe.oneshot(solver="CCSD")
             Es.update({frag_type: mbe.ebe_tot})
@@ -1403,7 +1403,7 @@ def run_indices_test(
         frag_type,
         target,
     ):
-        fobj = FragPart(frag_type=frag_type, be_type=be_type, mol=mf.mol)
+        fobj = fragpart(frag_type=frag_type, be_type=be_type, mol=mf.mol)
         try:
             assert fobj.fsites == target["fsites"]
             assert fobj.edge == target["edge"]
diff --git a/tests/hf-in-hf_BE_test.py b/tests/hf-in-hf_BE_test.py
index a5d6881c..3b08b053 100644
--- a/tests/hf-in-hf_BE_test.py
+++ b/tests/hf-in-hf_BE_test.py
@@ -10,7 +10,7 @@
 
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 
 class TestHFinHF_restricted(unittest.TestCase):
@@ -53,7 +53,7 @@ def test_octane_sto3g_ben(self):
     def molecular_restricted_test(self, mol, be_type, test_name, delta=1e-5):
         mf = scf.RHF(mol)
         mf.kernel()
-        fobj = FragPart(frag_type="autogen", be_type=be_type, mol=mol)
+        fobj = fragpart(frag_type="autogen", be_type=be_type, mol=mol)
         mybe = BE(mf, fobj)
         self.assertAlmostEqual(
             mybe.ebe_hf,
diff --git a/tests/kbe_polyacetylene_test.py b/tests/kbe_polyacetylene_test.py
index ba40c630..d3faa992 100644
--- a/tests/kbe_polyacetylene_test.py
+++ b/tests/kbe_polyacetylene_test.py
@@ -5,7 +5,7 @@
 import numpy as np
 from pyscf.pbc import df, gto, scf
 
-from quemb.kbe import BE, FragPart
+from quemb.kbe import BE, fragpart
 
 
 def test_polyacetylene():
@@ -50,7 +50,7 @@ def test_polyacetylene():
     kpoint_energy = kmf.kernel()
 
     # Define fragment in the supercell
-    kfrag = FragPart(be_type="be2", mol=cell, kpt=kpt, frozen_core=True)
+    kfrag = fragpart(be_type="be2", mol=cell, kpt=kpt, frozen_core=True)
     # Initialize BE
     mykbe = BE(kmf, kfrag, kpts=kpts)
 
diff --git a/tests/molbe_h8_test.py b/tests/molbe_h8_test.py
index 87f31d27..6e65a0cc 100644
--- a/tests/molbe_h8_test.py
+++ b/tests/molbe_h8_test.py
@@ -5,7 +5,7 @@
 import numpy as np
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 
 def prepare_system():
@@ -32,7 +32,7 @@ def prepare_system():
 
 
 def do_BE(mol, mf, be_type: str, only_chem: bool):
-    fobj = FragPart(be_type=be_type, mol=mol)
+    fobj = fragpart(be_type=be_type, mol=mol)
     mybe = BE(mf, fobj)
     mybe.optimize(solver="FCI", only_chem=only_chem)
     return mybe
diff --git a/tests/molbe_io_fcidump_test.py b/tests/molbe_io_fcidump_test.py
index 85cc75ac..ede232d2 100644
--- a/tests/molbe_io_fcidump_test.py
+++ b/tests/molbe_io_fcidump_test.py
@@ -11,7 +11,7 @@
 from pyscf.lib.misc import with_omp_threads
 from pyscf.tools import fcidump
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 from quemb.molbe.misc import be2fcidump, libint2pyscf
 
 
@@ -31,7 +31,7 @@ def prepare_system() -> BE:
         mf.kernel()
 
     # Construct fragments for BE
-    fobj = FragPart(be_type="be2", mol=mol)
+    fobj = fragpart(be_type="be2", mol=mol)
     oct_be = BE(mf, fobj)
     return oct_be
 
diff --git a/tests/molbe_octane_get_rdms_test.py b/tests/molbe_octane_get_rdms_test.py
index 62b47919..2dde6db2 100644
--- a/tests/molbe_octane_get_rdms_test.py
+++ b/tests/molbe_octane_get_rdms_test.py
@@ -4,7 +4,7 @@
 import numpy as np
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 
 # TODO: actually add meaningful tests for RDM elements,
 #   energies etc.
@@ -51,7 +51,7 @@ def test_rdm():
     mf.kernel()
 
     # initialize fragments (use frozen core approximation)
-    fobj = FragPart(be_type="be2", mol=mol, frozen_core=True)
+    fobj = fragpart(be_type="be2", mol=mol, frozen_core=True)
     # Initialize BE
     mybe = BE(mf, fobj)
 
diff --git a/tests/molbe_octane_test.py b/tests/molbe_octane_test.py
index de77e62e..f3dd3482 100644
--- a/tests/molbe_octane_test.py
+++ b/tests/molbe_octane_test.py
@@ -8,7 +8,7 @@
 import numpy as np
 from pyscf import gto, scf
 
-from quemb.molbe import BE, FragPart
+from quemb.molbe import BE, fragpart
 from quemb.shared.io import write_cube
 
 
@@ -17,7 +17,7 @@ def test_octane_molbe() -> None:
     mol, mf = prepare_octane()
 
     # initialize fragments (without using frozen core approximation)
-    fobj = FragPart(be_type="be2", mol=mol, frozen_core=False)
+    fobj = fragpart(be_type="be2", mol=mol, frozen_core=False)
     # Initialize BE
     mybe = BE(mf, fobj)
 
@@ -34,7 +34,7 @@ def test_cubegen() -> None:
     # Prepare octane molecule
     mol, mf = prepare_octane()
     # Build fragments
-    fobj = FragPart(be_type="be2", mol=mol, frozen_core=True)
+    fobj = fragpart(be_type="be2", mol=mol, frozen_core=True)
     # Run BE2
     mybe = BE(mf, fobj)
     mybe.optimize(solver="CCSD", nproc=1, ompnum=1)
diff --git a/tests/ube-oneshot_test.py b/tests/ube-oneshot_test.py
index b3f622f4..1827c008 100644
--- a/tests/ube-oneshot_test.py
+++ b/tests/ube-oneshot_test.py
@@ -11,7 +11,7 @@
 
 from pyscf import gto, scf
 
-from quemb.molbe import UBE, FragPart
+from quemb.molbe import UBE, fragpart
 
 
 class TestOneShot_Unrestricted(unittest.TestCase):
@@ -107,7 +107,7 @@ def molecular_unrestricted_oneshot_test(
     ):
         mf = scf.UHF(mol)
         mf.kernel()
-        fobj = FragPart(frag_type="autogen", be_type=be_type, mol=mol, frozen_core=frz)
+        fobj = fragpart(frag_type="autogen", be_type=be_type, mol=mol, frozen_core=frz)
         mybe = UBE(mf, fobj)
         mybe.oneshot(solver="UCCSD", nproc=1)
         self.assertAlmostEqual(