lmp: support unit real

[njzjz]

Fix #1262.

[codecov]

Codecov Report

Patch coverage: 87.50% and no project coverage change.

Comparison is base (835d6e5) 78.75% compared to head (8a4222e) 78.76%.
Report is 2 commits behind head on devel.

Additional details and impacted files

@@           Coverage Diff           @@
##            devel    #2775   +/-   ##
=======================================
  Coverage   78.75%   78.76%           
=======================================
  Files         242      242           
  Lines       25641    25653   +12     
  Branches     1517     1518    +1     
=======================================
+ Hits        20193    20205   +12     
  Misses       5058     5058           
  Partials      390      390           

Files Changed	Coverage Δ
source/lmp/pair_deepmd.cpp	54.06% <87.50%> (+0.66%)	⬆️

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[wanghan-iapcm]

The output of model deviations are also needed to be converted.