[Pw_forum] How to Fix certain atoms in relax calculation?

[lan haiping]

Hi ,

   i wanna do some  relaxation calculations with some atoms fixed, but i
donot know how to in PWSCF.
I have tried to read the Doc/INPUT_PW, and was confused that "if_pos(i)"
with 1 and CONSTRAINT CARDS might realize my goal.   Would you please give
me some hints about these two differences ?

 Regards,

Hai-Ping
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