Static screening
In this module you will learn how to calculate the static screening. This is the first step in the calculation of optical spectra within the Bethe-Salpeter framework.
Background
To calculate the correlation part of the kernel W we need the static dielectric screening. This is a calculation of the linear response of the system analogous to the calculation of the RPA/IP dielectric function. One important difference is that here we consider the static dielectric function.
Prerequisites
- You must first complete the "How to use Yambo" modules
You will need:
- The
SAVEdatabases for 3D hBN - The
yamboexecutable
Choosing input parameters
First, we need to initialize the yambo SAVE by just typing
$ yambo
Next, we generate the input by invoking yambo with the option "-X s" from the command line:
$ yambo -X s -F 01_3D_BSE_screening.in
The input opens in the standard editor. Similarly to the other linear response calculations the relevant input variables to be changed are:
% BndsRnXs 1 | 40 | % NGsBlkXs= 4000 mRy
The first variable gives how many bands are included in the sum to calculate the static response function. The second is a cutoff for the dimension of the static dielectric matrix.
In a subsequent tutorial you will see how to choose these two parameters. Another relevant input parameter to change is
% LongDrXs 1.000 | 1.000| 1.000 %
In this way the perturbing electric field has components in each direction.
Static screening runlevel
Run the calculation by invoking yambo:
$ yambo -F 01_3D_BSE_screening.in -J 3D_BSE
In the log of the calculation - found either in the file l_3D_BSE_screen_dipoles_em1s, if you used mpirun, or directly printed on the terminal, if you ran yambo as is - you can see that after calculating the dipole matrix elements, for each q vector yambo calculates the IP response function and by inversion the RPA response function
<02s> Xo@q[1] |########################################| [100%] --(E) --(X) <02s> X@q[1] |########################################| [100%] --(E) --(X)
In the report, r-3D_BSE_dipoles_em1s, the details of the calculations are reported under the 5th section
[05] Static Dielectric Matrix =============================
This calculation does not produce any human readable output, but both the dipole matrix elements and the static screening dielectric function are saved in a database in the 3D_BSE directory:
3D_BSE/ndb.dipoles 3D_BSE/ndb.em1s 3D_BSE/ndb.dipoles 3D_BSE/ndb.em1s_fragment_*
which are needed in the BS kernel runlevel.
Summary
From this tutorial you've learned:
- How to compute the static screening as first step in a BSE calculation
- Next module: Bethe-Salpeter kernel
- Back to Calculating optical spectra including excitonic effects: a step-by-step guide tutorial
- Back to technical modules menu
- Back to tutorials menu