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["Yunhee Chang" <yunhee.chang@kriss.re.kr>]

Dear Javier,

Thank you very much for your kind reply and explanations about my questions.
And I have two linked questions.

Q1) 
I considered only 20 atoms among 24 atoms to calculate the phonon frequencies,
so this error message is occured ... from your explanations.
I calculate the Si(001) surface, so this system has 20 Si atoms and 4 H atoms.
To know the Si(001) surface phonon band, the 4 H atoms is not important,
so I removed the 4 H atoms to calculate the dynamical matrix.
According to this error messages, shoul I have to add the 4 H atoms as well 
to calculate dynamical matrix?
If I removed 4 H atoms, is their phonon band not correct?

Q2)
You said, "Anyway often these incomplete dynamical matrices can be merged 
(using 
> MRGDDB) in some cases in order to get a bigger matrix that can be 
> analyzed with ANADDB..."
that means the when I merged the dynamical matrices, do that probelms 
disappear?
What does that mean the bigger matrix that can be analyzed with ANADDB?

Thank you again and I'm waiting for your reply~!

Best regards,
Yunhee Chang


----- Original Message ----- 
From: "Javier Torres" <javier.torres@unito.it>
To: <forum@abinit.org>
Sent: Monday, June 19, 2006 6:58 PM
Subject: Re: [abinit-forum] The dynamical matrix was incomplete : phonon 
frequencies may be wrong ...


> Dear Yunhee
> 
> The message that you obtain during the rf calculation is a consequence 
> of a incomplete dynamical matrix... A complete dynamical matrix is 
> generated considering the displacement of all the irreducible atoms in 
> your unit cell in the three cell directions...
> Ex:
> If you have 6 atoms in your unit cell you have to define
> 
> rfphon 1
> rfatpol  1 6      # it means from atom 1 to atom 6
> rfdir      1 1 1   # it means displacements along a, b and c directions
> 
> If your have atoms related by symmetry the calculation is performed only 
> for the irreducible set of atoms and directions, th ematrix then is 
> completed considering symmetry...
> 
> The message, that you observe, is displayed when you calculate the 
> phonon frequencies considering only some atoms or one direction; 
> therefore ABINIT tell you that the obtined phonons may be wrong... 
> Anyway often these incomplete dynamical matrices can be merged (using 
> MRGDDB) in some cases in order to get a bigger matrix that can be 
> analyzed with ANADDB...
> 
> Best Regards
> 
> F. Torres
> 
> 
>