[Pw_forum] regarding structural optimization

[kondaiah samudrala]

Dear all,

   I am doing test calculations for orthorhombic  layered compounds having
van der waals forces.  i calculated the volume by varying c/a, b/a and a
with energy and taken the minimum values of c/a, b/a and a. But my volume
change is surprisingly 2% with experimental ( even van der waals forces
having). I tried with the "vc-relax" for same system i found 12% volume
change with experimental.I tried with psedopotentials also and the results
are same.

I am very thankful any to solve this problem.

Thanks in advance

S.Appalakondaiah
Research Scholar
University of hyderabad
Hyderabad
India
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