[Pw_forum] Irreps and vibrational modes

Elie M elie.moujaes at hotmail.co.uk
Sat May 19 18:54:02 CEST 2012

A final question about that! Is there a way to check the frequencies of the Irreducible representations once each one is done or one has just to wait for the whole vibrational modes calculations to finish; The reason i am asking this is that since one might get negativefrequencies , I was wondering if I can check that before the whole calculation terminates (which takes 25 days) so I then can see what the problem is and lower the threshold if it is what is going wrong. Are those frequencies written to a file other than the output one?

Date: Mon, 14 May 2012 09:45:53 +0200
Subject: Re: [Pw_forum] Irreps and vibrational modes
From: lorenzo.paulatto at impmc.upmc.fr
To: elie.moujaes at hotmail.co.uk

On Mon, May 14, 2012 at 4:07 AM, Elie M <elie.moujaes at hotmail.co.uk> wrote:

(1) Are all the modes vibrational?
No, at Gamma you always have 3 translational modes of zero energy 

(2) Are any modes missing from the calculation like optical or accoustical modes? No 

(3) i did the calculation and got two of the modes negative which means either threshold is high or the ecutwav must be at least eight times ecutrho. Is a threshold of 10^(-15) still too high for such a system?

This is FAQ2 for phonon calculations: http://www.quantum-espresso.org/?page_id=366#7.2


ElieUniversity of NottinghamNG7 2RDUK 		 	   		  


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Lorenzo Paulatto IdR @ IMPMC/CNRS & Université Paris 6phone: +33 (0)1 44275 084 / skype: paulatzwww:   http://www-int.impmc.upmc.fr/~paulatto/
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