[gpaw-users] Intraband contributions in dielectric function calculations

[Kirsten Trøstrup Winther]

Dear Sharmila,

As Thomas explains, the intra-band contribution should only be added at 
q=0, since at finite q it is always included automatically. It looks 
like that you're now adding the extra contribution also at finite q, 
which does not make sense. Maybe this the reason that you're getting a 
weird result for the plasmon eigenmodes? The induced density should 
off-cause be zero in vacuum.

Also, have you remembered to truncate the Coulomb potential in the 
z-direction for 2D materials (to use truncation=2D)?

Best regards,
Kirsten

As Thomas

On 03/26/2016 09:38 PM, Thomas Olsen wrote:
>
> Dear Sharmila
>
> The intraband contributions to the response are included by the 
> "standard" response code at any finite q. The code does not really 
> distinguish between intraband and interband, but simply adds 
> contributions from pairs of occupied and unoccupied states. However, 
> q=0 is a limiting case where special care must be taken and an extra 
> term appears, which is essentially a Fermi surface integral of the 
> band velocities.
>
> BR
>
> Thomas
>
> ------------------------------------------------------------------------
> *Fra:* gpaw-users-bounces at listserv.fysik.dtu.dk 
> [gpaw-users-bounces at listserv.fysik.dtu.dk] på vegne af Sharmila 
> Shirodkar [sharmila.shirodkar86 at gmail.com]
> *Sendt:* 23. marts 2016 19:50
> *Til:* gpaw-users at listserv.fysik.dtu.dk
> *Emne:* [gpaw-users] Intraband contributions in dielectric function 
> calculations
>
> Dear All
>
> I have looked through the pair.py and chi0.py files in gpaw/response 
> folders.
> The condition for adding intraband contributions to the dielectric or 
> response matrix
> is given by
>
> optical_limit = not self.no_optical_limit and np.allclose(q_c, 0.0) 
> ------ (1)
>
> Implying that the intraband contributions are added only when q_c = 
> (0,0,0).
> Hence the dielectric matrix only contains the interband transitions.
> However, the paper "Plasmons in metallic monolayer and bilayer 
> transition metal dichalcogenides",
> Andersen et al, PHYSICAL REVIEW B 88, 155128 (2013) does report 
> plasmon dispersion with intraband contributions at non-zero q_c.
>
> I also changed the condition (1) to
>
> optical_limit = not self.no_optical_limit and self.intraband ----- (2)
>
> And made appropriate changes to chi0.py and pair.py files to 
> accommodate condition (2), as given below.
>
> A) In chi0.py
>     Line 139
>     replace  if np.allclose(q_c, 0.0):
>     with   if self.intraband:
>
>     Line 167
>     replace optical_limit = not self.no_optical_limit and 
> np.allclose(q_c, 0.0)
>     with   optical_limit = not self.no_optical_limit and self.intraband
>
> B) In pair.py
>     Line 757
>     replace optical_limit = not disable_optical_limit and 
> np.allclose(q_c, 0.0)
>     with      optical_limit = not disable_optical_limit and intraband 
> #SHARMILA
>
>     Line 916
>     replace assert np.allclose(pd.kd.bzk_kc[0], 0.0)
>     with assert np.allclose(0.0, 0.0)
>
> However, I was unable to reproduce the results of the above mentioned 
> paper.
> I observe that potential of the eigenmodes have a curvature (implying 
> that charge is not conserved, rho is non-zero (0.005) in vacuum).
> Please find the plots of potential and charge density (rho) of the 
> plasmon eigenmodes attached to this email.
>
> Any advice will be appreciated.
>
> Best Regards
> Sharmila Shirodkar
>
> Postdoctoral Research Fellow
> SEAS, Harvard University
> Cambridge, MA 02138
> USA
>
>
>
>
>
>
>
>
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