bug_fix | read "nelm" | compatible with vasp6 format change (#239)

* Update outcar.py

VASP6 writes NELMIN(minimum number of electronic steps) ahead of NELM(max num), 
dpdata reads the first line contains "NEIM", then will take the value of NELMIN as that of NELM, inducing "false" in scf_convergence_check

this revise includes this such cases by request a stronger check that the line should not be initiated by "NELMIN" or "NELMDL"

* bug_fix | read "nelm" | compatible with vasp6

adding a stricter check for whether the line is actually assigning value for  "NELM". 
expecting the assignment follows the format : 
```
"anywhere_in_the_line"+"NELM"+"any_number_of_spaces"+"="+"value(data-type-check_omitted_don't-believe-it's-needed-here)"+"whatever_else"
```

* Apply suggestions from code review

Co-authored-by: Jinzhe Zeng <[email protected]>

* Apply suggestions from code review

Co-authored-by: Jinzhe Zeng <[email protected]>

Co-authored-by: Han Wang <[email protected]>
Co-authored-by: Han Wang <[email protected]>
Co-authored-by: Jinzhe Zeng <[email protected]>

Author: 4 people

dpdata/vasp/outcar.py

@@ -1,10 +1,12 @@
 import numpy as np
+import re
 
 def system_info (lines, type_idx_zero = False) :
     atom_names = []
     atom_numbs = None
     nelm = None
-    for ii in lines: 
+    for ii in lines:
+        ii_word_list=ii.split()
         if 'TITEL' in ii : 
             # get atom names from POTCAR info, tested only for PAW_PBE ...
             _ii=ii.split()[3]
@@ -13,9 +15,11 @@ def system_info (lines, type_idx_zero = False) :
                 atom_names.append(_ii.split('_')[0])
             else:
                 atom_names.append(_ii)
-        elif 'NELM' in ii and nelm == None:
-            # will read only first nelm
-            nelm = int(ii.split()[2].rstrip(";"))
+        #a stricker check for "NELM"; compatible with distingct formats in different versions(6 and older, newers_expect-to-work) of vasp
+        elif nelm is None:
+            m = re.search(r'NELM\s*=\s*(\d+)', ii)
+            if m:
+                nelm = int(m.group(1))
         elif 'ions per type' in ii :
             atom_numbs_ = [int(s) for s in ii.split()[4:]]
             if atom_numbs is None :