Calculation of Opto-Electronic Properties of Orthorhombic Structure

This contribution is from my work of Magister's memoir.  

Electronic Properties:

1. Calculation of the band structure:

To calculate the band structure, one proceeds as follows:

1.      An SCF calculation is performed with optimal parameter values ​​for convergence of potential, energy and load density.

2.      We use the task called "BandStructure" on the w2web graphical interface and we click on the buttons one by one:

Ø   The Bi2S3.klist.band file is created from a few templates in the WIENROOT / SRC.templates directory. The band structure requires a different set of k-values ​​than that used to generate the density of states. For DOS, the code WIEN2k uses a mesh k stored in a file called "case.klist". For the structure band, the code WIEN2k generates another mesh k stored in a file called "case.klist_band". WIEN2k has in its stock meshes for precise paths for cubic (cs, bcc and fcc) and hexagonal structures; But if we want other paths for the previous structures or if we have other structures, we need to use the software "XCRYSDEN" to generate the mesh k for the desired path. Since the orthorhombic structure does not exist in the WIEN2k stock, XCRYSDEN was used to generate the necessary mesh for a desired path.

Ø   We calculate the eigenvalues ​​using the switch "-band" (this switch, taken by default, allows to read the mesh from the file Bi2S3.klist_band ( you may download this file from here )and not from the file Bi2S3.klist);

Ø   We edit the file Bi2S3.insp and we insert the energy of Fermi;

Ø   The band structure is calculated with "x spaghetti";

Ø   We represent the band structure with "plot bandstructure".

NB: To use the file xcrysden.klist you have to proceed as follows:

- Put the file in the working directory
- Select " from xcrysden " and click on the click on " Bi2S3.klist_band
- Continue with the other steps

2. Calculation of the Density of States DOS:

To calculate the density of the states, one proceeds as follows:

o  Perform a SCF calculation with the optimal parameters for convergence of potential, energy and load density.

o  Use a different mesh denser than other electronic properties. We use a mesh of 2000 points k using the subroutine "kgen" from the menu of "single programs";

o  Calculate the eigestates and the eigenenergies using the subprogram "LAPW1" from the menu of "single programs";

o  Calculate the valence densities and the Fermi energy using the subprogram "LAPW2" from the "single programs" menu;

o  The "DOS" task in the task menu is selected from the w2web GUI, and the buttons are clicked one by one:

Ø   Calculate the partial loads (x lapw2 -qt1);

Ø   Create the Bi2S3.int file as follows:

Bi2S3   -0.50     0.00200   1.500 0.003   EMIN, DE, EMAX, Gauss-broadening     18                              NUMBER OF DOS-CASES     0    1   Crystal               (atom,case,description)     1    1   Bi1 tot     1    2   Bi1 s     1    3   Bi1 p     1    7   Bi1 d     2    1   Bi2 tot     2    2   Bi2 s     2    3   Bi2 p     2    7   Bi2 d     3    1   S1  tot     3    2   S1  s     3    3   S1  p     4    1   S2  tot     4    2   S2  s     4    3   S2  p     5    1   S3  tot     5    2   S3  s     5    3   S3  p

Ø  Calculate partial state densities and total state density with "tetra";

Ø  Plot the densities of states  graphically with "dosplot".

3. Calculation of the Charge Density:

To calculate the electron density of valence, We proceed as follows:

o  Perform an SCF calculation with optimized parameters;

o  Select "El. Density" from the task menu on the w2web GUI;

Ø    The total charge density includes the Bi 5d states (semi-core states) and the resulting density around Bi would be very large and dominated by these states. In order to obtain a significant image of the effects of the chemical bond, these states must be eliminated. The inspection of the files Bi2S3.scf1 and Bi2S3.scf2 should allow us to choose the value Emin to eliminate the states of semi-core Bi 5d.

Ø   Recalculate the valence density with Emin = -O.5 Ry to eliminate the states 5d (x lapw2);

Ø   Choose a plane to represent the charge density (one chooses for example the plane (040) for the Bi2S3). The file Bi2S3.in5 is edited as follows:

Ø   Calculate the electronic density with "x lapw5";

Ø   Plot the electron density with "rhoplot" by choosing Ymin = 0.5 and Ymax = 

Optical Properties:

To calculate the optical properties for the TiC click on the link below:


http://wien2k-algerien1970.blogspot.nl/2016/10/calculation-of-optical-properties-of.html

Here we present the different input files for the orthorhombic structure:

 Bi2S3.inop

 99999 1         number of k-points, first k-point

-5.0  2.2         Emin, Emax for matrix elements

3                     number of choices (columns in *outmat) - 0: MME into  case.mme

1                     Re xx

2                     Re yy

3                     Re zz

OFF               ON/OFF   writes MME to unit 4

Bi2S3.injoint

1  9999 9999                             : LOWER,UPPER and (optional) UPPER-VAL BANDINDEX

 0.0000    0.00100   1.0000       : EMIN DE EMAX FOR ENERGYGRID IN ryd

eV                                             : output units  eV / ryd  / cm-1

     4                                           : SWITCH  

     3                                           : NUMBER OF COLUMNS

   0.1  0.1  0.3                           : BROADENING (FOR DRUDE MODEL - switch 6,7 -  ONLY)

Bi2S3.inkram

 0.1          Gamma: broadening of interband spectrum

 0.0          energy shift (scissors operator)

 0             add intraband contributions? yes/no: 1/0

12.60       plasma frequencies  (from joint, opt 6)

 0.20        Gammas for Drude terms