[Pw_forum] metal optimization tricks and constraining atomic position in a slab

[David Foster]

Dear Users and supporters

"....Thank you for your quick answers...."

I have two questions:

1- I prepared 3*3*3 bulk Pd super cell, and used "vc-relax". The relaxation needed 

   more than 200 iteration. I finally relaxed it with restarting command. Please help
   
   me in setting following parameters for fast relaxation for metals:
   
   a- degauss (I think increasing it helps for fast coarse optimization, but after it
   
      needs more fine optimization.
      with increasing it, does it need more "nbnd"?)

   b-mixing beta ( in my calculation, I set it to 0.3, but I got very fluctuation in optimization.
 
     does increasing it helps optimization speed?)

  c- I prepared input by a program that saves the structure in cif format. I used the coordination

     with "crystal" card. is it true?

2- I prepared 5 layers Pd slab and should fix two layers' coordination, but I don't know how.
    I read input style help but confused.

Thanks again 
Regards

David Foster

Ph.D. Student of Chemistry