QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: chethankumar_m on October 18, 2016, 09:03

Title: negative phonon in phonon band structure
Post by: chethankumar_m on October 18, 2016, 09:03

Hello
 I have calculated phonon band structure of graphene using classical potential but, in phonon band structure ZA band near Gamma position going negative. In reported result, it is positive only. how to solve this?

Title: Re: negative phonon in phonon band structure
Post by: Petr Khomyakov on October 18, 2016, 10:48

Could you attach the python script related to this phonon calculation? Which 'reported result' do you refer to? Was this 'reported result' obtained with the same classical potential you have adopted in ATK Classical for carbon?

Title: Re: negative phonon in phonon band structure
Post by: Julian Schneider on October 18, 2016, 12:04

We don't know the details of your system, but have you tried optimizing the configuration before calculating the phonon band structure?
That might remove the unstable modes ( which are, at least in my case, not at gamma ).

Title: Re: negative phonon in phonon band structure
Post by: chethankumar_m on October 18, 2016, 16:50

Thank you

Title: Re: negative phonon in phonon band structure
Post by: ams_nanolab on October 26, 2016, 18:25

It goes away with optimization. But keep in mind that you optimize with DFT first.

Title: Re: negative phonon in phonon band structure
Post by: quantumtoday on February 3, 2017, 16:28

it seems very hard to remove negative bands if using the potential tersoff_C_2010 (even the structure was optimized). Did you succeed in using this potential?

My concern is that is there any rule when optimizing structures to be sure that negative bands will go away just by one or two times of optimization?