[Pw_forum] Dynamical matrix diagonalization: rdiagh vs rdiaghg

[Alexandr Fonari]

Got it now,

Thanks a lot, Paolo.

> > On Tue, 2013-07-02 at 06:48 -0700, Alexandr Fonari wrote:

> > However, in Gamma code (I realize its deprecated

> it's not (yet) "deprecated", it is just an old piece of code 
> that has many limitations and few (or maybe zero) users

> > Can someone explain the differences between two resulting 
> > sets of eigenvectors?

> it's plain linear algebra. In one case, you solve 
> C*v=\omega M*v, where C_{\alpha i,\beta j} is the matrix of
> force constants; M_{\alpha i,\beta j} is the matrix of masses,
> in the base of (orthonormal) displacement modes "u" as used in 
> the code. If modes are the displacement of a single atom
> along a single cartesian component, the matrix M is diagonal.
> 
> In the other case, you solve D*w=\omega w, in cartesian axis;
> D_{\alpha i,\beta j}=C_{\alpha i,\beta j}/sqrt{m_i}/sqrt{m_j}
> is the dynamical matrix. 
> 
> Apart from phases, the only difference once you bring the v
> vectors in cartesian axis should be a factor sqrt{m_i}