add bcc interstitial calculation and change some default parameters in lmp

[kevinwenminion]

1. Add bcc interstitial calculations for transition metals which have six types of interstitial positions.
2. In lmp relaxation, change the convergence to be controlled by the force criteria. This is more reasonable, especially for large systems.
3. Change the "pair_coeff" in lmp to be compatible with the latest lmp version.

[codecov-commenter]

Codecov Report

Merging #696 (fc531a8) into devel (9e3b958) will decrease coverage by 0.20%.
The diff coverage is 4.42%.

@@            Coverage Diff             @@
##            devel     #696      +/-   ##
==========================================
- Coverage   33.94%   33.73%   -0.21%     
==========================================
  Files          86       86              
  Lines       15424    15525     +101     
==========================================
+ Hits         5235     5237       +2     
- Misses      10189    10288      +99     

Impacted Files	Coverage Δ
dpgen/auto_test/Interstitial.py	6.71% <0.00%> (-3.56%)	⬇️
dpgen/auto_test/common_equi.py	61.59% <30.00%> (+0.11%)	⬆️
dpgen/auto_test/lib/lammps.py	27.12% <40.00%> (ø)

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[wanghan-iapcm]

Could you please add a UT for added the BCC interstitial?

[kevinwenminion]

Could you please add a UT for added the BCC interstitial?

Yes, I will add the unittest.

[kevinwenminion]

BCC interstitial unittest has been added.