[Pw_forum] Example-29, "NOTE : eigenvalues are not computed without ortho."

[Paolo Giannozzi]

joaquin peralta wrote:

> The eigenvalues are not calculated, but why?

I know close to nothing on this specific subject, but, as a rule,
in CP the eigenvalues are obtained as a byproduct of iterative
orthonormalization (from diagonalization of the "Lambda" matrices,
i.e. Lagrange multipliers enforcing orthonormalization constraints).
If you use Gram-Schmidt orthonormalization, you do not have these
matrices. Nothing would prevent the calculation of eigenvalues by
some other algorithms (e.g. Davidson diagonalization), but as a
matter of facts, this is not currently implemented in CP. It is a
problem of "tradition", so to speak. Gram-Schmidt is inefficient and
should nbot be used anyway, except in the first few time steps.

Paolo
-- 
Paolo Giannozzi, Democritos and University of Udine, Italy