[Pw_forum] questions about vc-relax

[Huiqun Zhou]

dear list-users,

I'm trying to run vc-relax or vc-md calculation on a mineral using pw.x, and my purpose is to
investigate what kind of structrues it would evolve into upon applying a serise of pressures.
I know that because of finite-size effect the transition pressure determined this way is 
meaningless. I just want to get the possible structures and then use total energy calculations
for different phases to determine the transition pressures at 0K. 

But firstly I need to make clear the following questions:

(1) I think, for my purpose, I may need to use vc-relax, but what's the differences between 
  vc-relax and vc-md method in the implementation because the PR dynamics is the same
  for both methods (am I wrong)?
(2) Should I always set ibrav = 14 (trilinic system) for variable cell calculation?
(3) Although in the manual INPUT_PW, tempw in &ION, press, wmass in &CELL are said to 
  be used in MD runs, they also can be used in vc-relax runs (for controlling temperature), right?

Thanks!

Huiqun Zhou
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