[Pw_forum] pressure from pw calculation

[W. YU]

Dear pw users,

How do I get pressure value from pw calculation?

Is the value P in kbar from the "stress" subroutine
output (by giving the .tstress=.true. keywords in
$control input) supposed to be the pressure? Is it
trustworthy or I have to calculate pressure from
energy derivitive?

I put this quesiton here just because I found
something strange in my calculation. I calculated the
energy as a function of lattice parameter,then fitted
them to Murhaghan equation of state and got the
minimum energy lattice parameter. The fitted zero
pressure is also corresponds to the this lattice
parameter. But when I put "tstress=.true." keyword in
the input, the output P is a very large negtive value
at the fitted zero pressure lattice parameter. What's
wrong here, or just I have some misunderstanding?

best wishes

YU
    


		
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