[ase-users] how to get the pressure

[陈冠宇]

hi, my scribe like this:

from ase import Atoms 
from gpaw import GPAW 
import numpy as np 

a= Atoms('H2', positions=[(0, 0, 0), (0, 0, 1.1)], 
           calculator=GPAW()) 
 stress=a.get_stress() 
print  stress

there is a NotImplementedError ,after i run this scribe.
Traceback (most recent call last):
  File "h2.py", line 10, in <module>
    stress=a.get_stress()
  File "/usr/local/lib/python2.6/dist-packages/ase/atoms.py", line 586, in get_stress
    stress = self._calc.get_stress(self)
  File "/usr/local/lib/python2.6/dist-packages/gpaw/aseinterface.py", line 78, in get_stress
    raise NotImplementedError
NotImplementedError


what does it mean?  what should i do to get the pressure of system?
Sincerely, 
chen
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