[Pw_forum] negative el-ph coupling constant lambda

[陳 少華]

Dear Eyvaz,

Thank you very much,I will try these two factors.

max
--- Eyvaz Isaev <eyvaz_isaev at yahoo.com> 說：

> Dear Max,
> 
> One can see that \lambda you got is quite small,
> just
> around zero. So, a reason might be numerical noise
> for
> such a kind small \lambda. \gamma depends also on
> production of two delta functions which couples two
> electronic states at the Fermi Surface and it
> converges slowly. I suggest you should perform tests
> with respect to number of k-points (more fine that
> you
> used), and higher cutoff energies.  
> 
> Bests,
> Eyvaz.
> P.S. Just today I have got \lambda for a metal,
> around
> 0.5, and everything went smoothly.
> 
> --- 陳 少華 <chen_shao_hua197 at yahoo.com.tw> wrote:
> 
> > Dear Eyvaz and forum's members,
> > 
> > When I calculated the el-ph coupling constant
> > \lambda
> > of material.I find some negative value
> > 
> >   Electron-phonon coupling constant, lambda
> > 
> >  Broadening   0.0100 lambda       0.0008 dos_el  
> > 0.3719
> >  Broadening   0.0200 lambda       0.0012 dos_el  
> > 0.3674
> >  Broadening   0.0300 lambda       0.0021 dos_el  
> > 0.3565
> >  Broadening   0.0400 lambda      -0.0098 dos_el  
> > 0.3821
> >  Broadening   0.0500 lambda      -0.0303 dos_el  
> > 0.5231
> >  Broadening   0.0600 lambda      -0.0394 dos_el  
> > 0.7545
> >  Broadening   0.0700 lambda      -0.0408 dos_el  
> > 1.0409
> >  Broadening   0.0800 lambda      -0.0382 dos_el  
> > 1.3767
> >  Broadening   0.0900 lambda      -0.0333 dos_el  
> > 1.7603
> >  Broadening   0.1000 lambda      -0.0274 dos_el  
> > 2.1824
> > 
> > Also find some negative value in gam.line
> > e.g.
> >   24     0.0000  0.0000  0.0000  -0.0001  0.0000
> > -0.0001    *****    0.0000  0.0000
> > 
> > But no negative frequency found in matdyn.freq
> > 
> > I thought -\lambda comes from -\gamma (phonon
> > linewidth), and -\gamma  comes from -\omega
> > (frequency) by its definitions.
> > 
> > So I wonder why I got -\lambda and -\gamma (It
> > should
> > be >=0)
> > even frequency \omega seems fine (no negative) ???
> > 
> > Should I just try check convergence of \gamma in
> > dependent on cutoff energy and k-points sampling ?
> > (from forum's "search archive", title " 3
> questions
> > about elph file of Calculation of electron-phonon
> > interaction coefficients" suggestions )
> > 
> > Thanks in advance
> > 
> > max
> > PHD candidate
> > Physics department, National Taiwan
> > University,Taiwan
> > 
> > 
> >      
> >
>
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> >
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> 
> 
>
-------------------------------------------------------------------
> Prof. Eyvaz Isaev, 
> Theoretical Physics Department, Moscow State
> Institute of Steel & Alloys, Russia, 
> IFM, Linkoping University, Sweden 
> Condensed Matter Theory Group, Uppsala University,
> Sweden 
> Eyvaz.Isaev at fysik.uu.se, eyvaz_isaev at yahoo.com
> 
> 
>      
>
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