How to treat low dimensional systems: Difference between revisions

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*  Run [[Initialization]]
*  Run [[Initialization]]


==Generate the box-like  ==
==Generate the cutoff databases (yambo -r)==
To simulate an isolated nano-material a convergence with cell vacuum size is in principle required, like in the DFT runs.
To simulate an isolated nano-material a convergence with cell vacuum size is in principle required, like in the DFT runs.


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  cylindrical cutoff (for 1D systems)
  cylindrical cutoff (for 1D systems)
  box-like    cutoff (for 0D, 1D and also 2D systems)
  box-like    cutoff (for 0D, 1D and also 2D systems)
In this tutorial we learn how to use the box-like cutoff for a 2D system with the non-periodic direction along z.
In this tutorial we learn how to use the box-like cutoff for a 2D system with the non-periodic direction along z.


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[[File:Vc4.png|none|500px|]]
[[File:Vc4.png|none|500px|]]
Important remarks:
Important remarks:
== Generate the cutoff database (yambo -r) ==
   the Random Q-points integration technique is required  
   the Random Q-points integration technique is required  
   choose L_i sligthly smaller than the cell size in the i-direction
   choose L_i sligthly smaller than the cell size in the i-direction


== Generate the cutoff database (yambo -r) ==
== Create the input ==


Creation of the input file:
Creation of the input file:
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Close the input file and run yambo
Close the input file  
 
==run yambo==


  $ yambo -F  yambo_cut2D.in  -J 2D
  $ yambo -F  yambo_cut2D.in  -J 2D

Revision as of 11:09, 26 March 2017

In this tutorial you will learn (for a 2D material) how to:

  • generate a coulomb potential with a box-like cutoff in the non-periodic direction
  • visualize this coulomb potential
  • use this cutoff in the HF, GW and BSE calculation
  • analyze the difference with similar calculations without cutoff

Prerequisites

Generate the cutoff databases (yambo -r)

To simulate an isolated nano-material a convergence with cell vacuum size is in principle required, like in the DFT runs.

The use of a truncated Coulomb potential allows to achieve faster convergence eliminating the interaction between the repeated images along the non-periodic direction (see i.e. D. Varsano et al Phys. Rev. B and .. )

In YAMBO you can use :

spherical   cutoff (for 0D systems)
cylindrical cutoff (for 1D systems)
box-like    cutoff (for 0D, 1D and also 2D systems)

In this tutorial we learn how to use the box-like cutoff for a 2D system with the non-periodic direction along z.

The Coulomb potential with a box-like cutoff is defined as

Vc1.png

Then the FT component is

Vc2.png

where

Vc3.png

For a 2D-system with non period direction along z-axis we have

Vc4.png

Important remarks:

Generate the cutoff database (yambo -r)

 the Random Q-points integration technique is required 
 choose L_i sligthly smaller than the cell size in the i-direction

Create the input

Creation of the input file:

$ yambo -F yambo_cut2D.in  -r

Open the input file yambo_cut2D.in

Change the variables inside as:

RandQpts= 1000000          # [RIM] Number of random q-points in the BZ
RandGvec= 100        RL    # [RIM] Coulomb interaction RS components
CUTGeo= "box z"            # [CUT] Coulomb Cutoff geometry: box/cylinder/sphere X/Y/Z/XY..
% CUTBox
 0.00     | 0.00     | 32.0    |        # [CUT] [au] Box sides


Close the input file

run yambo

$ yambo -F  yambo_cut2D.in  -J 2D