[Pw_forum] regarding structural optimization

[GAO Zhe]

Because of your question without any details, I can only answer it generally. For getting convergency lattice parameter by energy-volume method, you can read the paper,Acta Materialia 54 (2006) 1641-1657, in which the author discussed that issue by Wien2k code. Or, if you want to use "vc-relax", you'd better decrease the convergence threshold to very small number with convergence cutoff energy, k-mesh and so on.
One more to be noted is that the minimum energy configuration corresponds to zero force, but minimum enthalpy corresponds to zero force and stress. In "vc-relax" case, we try to find zero both for force and stress instead of only for total energy.


--
GAO Zhe
CMC Lab, MSE, SNU, Seoul, S.Korea


At 2011-09-14 17:14:08,"kondaiah samudrala" <konda.physics at gmail.com> wrote:
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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