[QE-users] Raman output displaying stars

[Lorenzo Paulatto]

Hello,
if I remember correctly, a k-point grid that includes the K point 
invariably causes problems in graphene. This is because graphene is 
metallic at this point, its Raman tensor diverges.

To have the Raman tensor correctly, you should use a much larger grid 
and take care to not include the K-point, i.e. the grid dimension must 
not be a multiple of 3. I recommend trying 64x64x1

regards


On 4/19/20 4:58 PM, grayj6 at rpi.edu wrote:
> I am having an issue computing the Raman spectrum for graphene. The 
> output is as follows:
> <#>
> 
> # mode   [cm-1]    [THz]      IR          Raman   depol.fact
> 
>      1  -4834.05 -144.9213    0.0000***************    0.7500
> 
>      2     -0.00   -0.0000    0.0000***************    0.7500
> 
>      3     -0.00   -0.0000    0.0000***************    0.7500
> 
>      4      0.00    0.0000    0.0000***************    0.7500
> 
>      5      0.00    0.0000    0.0000***************    0.7500
> 
>      6      0.00    0.0000    0.0000***************    0.7500
> 
> 
> I did the relaxation and scf calculations using LDA, with a cutoff of 
> 120 Ry, and force convergence of 1.0d-6, etot convergence of 1.0d-8, and 
> electronic convergence of 1.0e-10. I used a 30 30 1 kpoint grid and used 
> the grimme-d2 van der waals option. I also did not include smearing as 
> the phonon calculation yelled at me when I tried. I am using a two atom 
> cell, is this the problem?
> 
> 
> 
> 
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-- 
Lorenzo Paulatto - Paris