[Pw_forum] GWW-band (P. Umari)

[Geoffrey Stenuit]

Dear Ali,

Just a few additional words:
The symmetric dielectric matrix is given in the output file generated  
by the binary head.x (based on the ph.x phonon code as Paolo said). In  
particular, it is also given by the second number on the line starting  
by "HEAD:" .
In other words, if you do a "grep HEAD: output_file_name", you will  
obtain a list with three columns. The first will be "HEAD:", the  
second column will give the imaginary frequency at which the symmetric  
dielect. constant has been calculated, and the third will give the  
dielect constant.
You should have n_gauss+1 lines.
The convergence of these values should be checked as a function of the  
k-point sampling.

Good luck,

Joe



Quoting umari at democritos.it:

> Dear Ali,
>
> First of all, note that the GWW is implemented only at the gamma point,
> so it requires large supercells, (or better it is appropriate for
> non-crystalline systems).
> However the long-range parts of the symmetric dielectric matrix
> and of the screened-interaction can be calculated using k-points.
> With the code ph.x you are calculating the head and the wings of
> the symmetric dielectric matrix.
> E_HEAD are the head terms of the symmetric dielectric matrix
> calculated on the imaginary frequency axis (e.g. "E_HEAD : 58"
> is relative to the 58th frequency step). These terms together with
> the wings are calculated using linear response.
> Then, also the long range part  (element G=0,G=0)
> of the screened interaction can also be calculated using a k-points grid.
> The calculated elements are <\Psi_i|G(i \tau)v|\Psi_i>,
> where \Psi_i are the KS states G(i\tau) is the KS Green function
> in imaginary time and v is the bare Coulomb interaction.
> The term "X energy 1" is the exchange energy relative to the 1st KS state.
>
>> I am trying to use implemented approach GWW in espresso to obtain
>> quasiparticle state for bulk TiO2 ,but I didn,t succeed to get true band
>> gap by GW density of state.
>> I used 10 10 12 kmesh for k sampling but I don't know which file and which
>> rows contains dielectric constant. when I grep E_HEAD ,the last lines is
>> E_HEAD : 58 (-0.288322417972075195E-19,-0.347622164532722579E-06)
>> E_HEAD : 59 (0.136048521030191330E-19,-0.268035068560476896E-06)
> ..... .....
>> what is these two columns? where do I look for dielectric constant?
>> also when I grep the energy in exchange file I see
>> X energy 1 -3.13056306094735648
>> X energy 2 -3.13125888267243768
>
> Best regards,
>
> P. Umari (Democritos)
>
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