How do I surface force constant from bulk force constants?

Message

nfs21cn · #1 Post by **nfs21cn** » Tue Sep 05, 2006 2:18 am

From vasp I can get force constant matrix, but I need surface force constant.
How can I do that?
Plz help me

bandy · #2 Post by **bandy** » Thu Sep 07, 2006 6:42 pm

The size of force constant matrix(dynamical matrix) will depend on degrees of freedom calculated from POSCAR counting Ts at the right side. You can obtain force constant matrix from forces by writing a simple numerical finite difference code, or put write statement in vasp src and then recompile.

nfs21cn · #3 Post by **nfs21cn** » Wed Sep 13, 2006 3:28 pm

Sorry, I can't understand "... Ts at the right side"
3x

bandy · #4 Post by **bandy** » Wed Sep 13, 2006 4:31 pm

nfs21cn wrote:

Code: Select all

Sorry, I can't understand "... Ts at the right side"
3x;

I do not understand what you mean by this. But once you
get forces for displacements of atoms, then you can get
force constants by finite difference method.

I hope that helps.

tjf · #5 Post by **tjf** » Fri Sep 22, 2006 4:40 pm

I think bandy is referring to the selective dynamics specifications. No selective dynamics gives 3.N