How to treat low dimensional systems
In this tutorial you will learn how to:
- generate a truncated coulomb potential with a box-like cutoff
- use this truncated coulomb in the HF, GW and BSE calculation
- analyze the difference with corresponding calculations without this cutoff
Prerequisites
- Complete the Generating the Yambo databases tutorial
SAVEfolder for 2D hBN.yamboexecutableyppexecutable- Run Initialization
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 this tutorial we learn how to generate a box-like cutoff for a 2D system with the non-periodic direction along z.
In YAMBO you can use :
spherical cutoff (for 0D systems) cylindrical cutoff (for 1D systems) box-like cutoff (for 0D, 1D and 2D systems)
The Coulomb potential with a box-like cutoff is defined as
Then the FT component is
where
For a 2D-system with non period direction along z-axis we have
Important remarks:
- the Random Integration Method (RIM) is required to perform the Q-space integration
- for sufficiently large supercells a choose L_i slightly smaller than the cell size in the i-direction ensure to avoid interaction between replicas
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
in the directory 2D you will find the two new databases
ndb.RIM ndb.cutoff