[Pw_forum] How to fix some atoms in the ph.x calculation

[Xunlei Ding]

Dear all,

An molecule is adsorbed on a surface. I just want to calculate the 
vibrational frequencies of the molecule (and a few atoms in the first 
layer).
How can I fix the other atoms in the ph.x calculation? I found "nrapp", 
"nat_todo" in the INPUT_PH, but I don't know whether they can be used 
for this purpose, and how to use them. Thank you!

Yours sincerely,
Ding