[Pw_forum] bulk module (orthorhombic)

[Lorenzo Paulatto]

On Mon, May 4, 2009 11:03, meghdad saeedian wrote:
>  Dear all,
>
>  How can I calculate the bulk module for an orthorhombic lattice  with
>  espresso?

Dear Saeedian,
as far as I know, there is no ready-made program in QE that can compute
the Bulk modulus from, let's say, an energy-volume curve (there is ev.x in
pwtools, but it can only handle cubic and hcp systems).

the easier way to get the bulk modulus is, in my opinion, to do several
scf calculation around the equilibrium lattice parameters (let's say less
than 1% avay) and then compute:
  B = -V \partial p \over \partial V
by hand. The system can in principle be anisotropic, so take care to
perturb it along all inequivalent axis. In order to have the pressure
printed you must set tpstress=.true. in the control namelist.

If you want to be more sophisticated you can use some more accurate
equation of state, i.e.
<http://en.wikipedia.org/wiki/Birch–Murnaghan_equation_of_state>.

regards

-- 
Lorenzo Paulatto
SISSA  &  DEMOCRITOS (Trieste)
phone: +39 040 3787 511
skype: paulatz
www:   http://people.sissa.it/~paulatto/



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