[Pw_forum] Question about P= pressure

[Bipul Rakshit]

Dear PWSCF users,
I am doing calculation on Mg2Si. There I just want to plot Pressure vs
Volume graph.
So what i did, first I found the equilibrium lattice constant (P=0.0),
then I reduce the lattice parameter, so the pressure increases.

With that Volume vs Pressure data, I plot the graph. But when i
compared with experimental VvsP, it is not at all matching.
Infact my volume is far less than the experimental value.

So my question is, the pressure term which we get at the end of scf
run, is the pressure on the system?
If the pressure is equivalent to the pressure on the system, so why I
am getting such large deviation (cal. volume is very less than expt,)?

Please help me in this matter.
-- 
Bipul Rakshit
PhD Student,
Barkatullah University,
Bhopal 462026,
MP, India