[Pw_forum] frc_blk question

[wlyim at puccini.che.pitt.edu]

Dear all,

I tried to calculate the phonon structures of surfaces in (1x1) and (2x2) 
supercells. However, I encountered a problem of violating the Hermitian of 
dynamical matrix on the (2x2) model, while the (1x1) model had no problem.

A warning from matdyn.x read like:
     Max |d(i,j)-d*(j,i)| =  0.008889
     Max |d(i,j)-d*(j,i)|/|d(i,j)|:  10.7732%

When I comment the lines calling "frc_blk" in "setupmat" subroutine, the 
warning disappeared.
!     call frc_blk (nax_blk,dyn_blk,qp,tau_blk,nat_blk,              &
!          &              nr1,nr2,nr3,nrx,frc,at_blk,bg_blk,rws,nrws)

Can anyone help me to clarify what "frc_blk" routine doing?

Many thanks in advance.

Best regards,
William