[Pw_forum] questions about negative charge and extrapolation

[Paolo Giannozzi]

On Feb 8, 2007, at 12:42 , Eduardo Ariel Menendez P wrote:

> I am curious about these  warning messages
>
>     Writing output data file cdteo3_80-3000p.save
>      Check: negative starting charge=   -0.400082
> Is it due to the FFT? The total charge is 576

no, it is explained here:
http://www.democritos.it/pipermail/pw_forum/2003-April/000207.html

>      Message from extrapolate_wfcs:
>      the matrix <psi(t-dt)|psi(t)> has 69 zero eigenvalues
>
> does it means that is better no to extrapolate?

well....there is a "alignment" procedure to be performed on the
wavefunctions psi(t) and psi(t-dt) in order to make the extrapolation.
A zero eigenvalue signals that is a psi(t) that has no overlap with
any of the psi(t-dt) (or at least, this is what I remember). If it
happens for one or a few of the high-lying levels, it is quite normal.
If it happens for 69 wavefunctions, it is definitely NOT normal...

Paolo
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Paolo Giannozzi, Democritos and University of Udine, Italy