Dear PyXtal_FF developers

I'm a new to the PyXtal_FF, and I checked the examples in PyXtal_FF/examples.

I tried to run /examples/Si-Python/bp-NN.py

python3 bp-NN.py

the following error had occurred.

        ______       _    _          _         _______ _______ 
          (_____ \     \ \  / /        | |       (_______|_______)
           _____) )   _ \ \/ / |_  ____| |        _____   _____   
          |  ____/ | | | )  (|  _)/ _  | |       |  ___) |  ___)  
          | |    | |_| |/ /\ \ |_( ( | | |_______| |     | |      
          |_|     \__  /_/  \_\___)_||_|_(_______)_|     |_|      
                 (____/      


    A Python package for Machine Learning Interatomic Force Field
     Developed by Zhu's group at University of Nevada Las Vegas
The source code is available at https://github.com/qzhu2017/FF-project

=========================== version 0.1.8 =============================

Descriptor parameters:
type : BehlerParrinello
Rc : 5.0
cutoff : cosine

Features and precomputed descriptors exist: Si-BP/Train_db.dat

25 structures have been loaded.
Computing the descriptors...
Traceback (most recent call last):
File "bp-NN.py", line 40, in
ff.run(mode='train', TrainData=TrainData, TestData=TestData)
File "/usr/local/lib/python3.8/dist-packages/pyxtal_ff-0.1.8-py3.8.egg/pyxtal_ff/init.py", line 276, in run
testDB.store(TestData, self._descriptors, True, self.path+'ase.db')
File "/usr/local/lib/python3.8/dist-packages/pyxtal_ff-0.1.8-py3.8.egg/pyxtal_ff/utilities/init.py", line 104, in store
self.add(function, data)
File "/usr/local/lib/python3.8/dist-packages/pyxtal_ff-0.1.8-py3.8.egg/pyxtal_ff/utilities/init.py", line 140, in add
for i, d in enumerate(p.imap_unordered(func, _data)):
File "/usr/lib/python3.8/multiprocessing/pool.py", line 868, in next
raise value
File "/usr/lib/python3.8/multiprocessing/pool.py", line 537, in _handle_tasks
put(task)
File "/usr/lib/python3.8/multiprocessing/connection.py", line 206, in send
self._send_bytes(_ForkingPickler.dumps(obj))
File "/usr/lib/python3.8/multiprocessing/reduction.py", line 51, in dumps
cls(buf, protocol).dump(obj)
TypeError: cannot pickle '_dbm.dbm' object

Same errors also occurred in SiO2-Python.

I had checked unit test of pyxtal_FF (python pyxtal_ff/test_all.py ) and in this case, errors did't occurred.

My environment are
Python 3.8.10
numba 0.54.1
numpy 1.20.3
torch 1.10.0
monty 2021.8.17
seekpath 2.0.1
ase 3.22.0

What is wrong for my environment ?

Sincerely,

Yukihiro Okuno.