Wannier90

Wannier90 is a useful package to generating the maximally-localized Wannier functions (MLWFs), which can be used to compute advanced electronic properties. Some post-processing tools (such as WannierTools, etc.) will use MLWFs for further analysis and calculations.

Currently ABACUS provides an interface to Wannier90 package. The users are assumed to be familiar with the use of Wannier90. The ABACUS-Wannier90 interface is only suitable for nspin=1 or 2, not for nspin=4 or spin-orbit coupling (SOC).

To construct the MLWFs using the wave functions of ABACUS generally requires four steps. Here we use the diamond as an example which can be found in examples/interface_wannier90/.

1. Enter the ABACUS_towannier90/ folder, prepare a Wannier90 input file diamond.win, which is the main input file for Wannier90. Then To generate diamond.nnkp file by running Wannier90, which ABACUS will read later:

   wannier90 -pp diamond.win
   

   The content of diamond.win is as follows:

   num_wann        =  4
   num_iter        = 20
   
   wannier_plot=.true.
   wannier_plot_supercell = 3
   wvfn_formatted = .true.
   
   begin atoms_frac
   C   -0.12500  -0.1250    -0.125000
   C    0.12500   0.1250     0.125000
   end atoms_frac
   
   begin projections
   f=0.0,0.0,0.0:s
   f=0.0,0.0,0.5:s
   f=0.0,0.5,0.0:s
   f=0.5,0.0,0.0:s
   end projections
   
   begin unit_cell_cart
   -1.613990   0.000000   1.613990
    0.000000   1.613990   1.613990
   -1.613990   1.613990   0.000000
   end unit_cell_cart
   
   mp_grid : 4 4 4
   
   begin kpoints
   0.0000  0.0000     0.0000
   0.0000  0.2500     0.0000
   0.0000  0.5000     0.0000
   0.0000  0.7500     0.0000
   ...
   end kpoints
   

2. Do a self-consistent calculation and get the converged charge density:

   cp INPUT-scf INPUT
   cp KPT-scf KPT
   mpirun -np 4 abacus
   

3. Do a non-self-consistent calculation:

   cp INPUT-nscf INPUT
   cp KPT-nscf KPT
   mpirun -np 4 abacus
   

   below are the INPUT file (nscf):

   INPUT_PARAMETERS
   
   ntype                   1
   ecutwfc                 50
   nbands                  4
   calculation             nscf
   scf_nmax                50
   pw_diag_thr             1.0e-12
   scf_thr                 1.0e-15
   init_chg                file
   symmetry                0
   towannier90             1
   nnkpfile                diamond.nnkp
   

   There are seven interface-related parameters in the INPUT file:

   • towannier90: 1, generate files for wannier90 code; 0, do not generate.

   • nnkpfile : the name of the file generated by running “wannier90 -pp …”.

   • wannier_spin: If you use nspin=2, up: calculate the Wannier functions for the spin up components ; down: calculate the Wannier functions spin down components.

   • out_wannier_mmn: control whether to output the “*.mmn” file.

   • out_wannier_amn: control whether to output the “*.amn” file.

   • out_wannier_eig: control whether to output the “*.eig” file.

   • out_wannier_unk: control whether to output the “UNK.*” file.

   • out_wannier_wvfn_formatted: control what format of the Wannier function file to output, true: output the formatted text file; false: output the binary file. Note that the wvfn_formatted option in *.win file (input file of Wannier90) has to be set accordingly with this option.

   Note: You need to turn off the symmetry during the entire nscf calculation.

   To setup the KPT file according to the diamond.win file, which is similar to “begin kpoints …” in the diamond.win file:

   K_POINTS
   64
   Direct
   0.0000 0.0000 0.0000 0.0156250
   0.0000 0.2500 0.0000 0.0156250
   0.0000 0.5000 0.0000 0.0156250
   0.0000 0.7500 0.0000 0.0156250
   ...
   

   After the nscf calculation, ABACUS will generate diamond.amn, diamond.mmn, diamond.eig, UNK files in the OUT. folder which are input files needed by Wannier90 code.

4. Copy .amn, .mmn, .eig, UNK file to wannier/ folder, to get the MLWFs by running Wannier90:

   wannier90 diamond.win
   

Notes:

• The ABACUS-wannier90 interface can be used in both PW and LCAO basis.

• If you want to plot the Wannier function, you must set wvfn_formatted = .true. in diamond.win, otherwise Wannier90 code cannot read files generated by ABACUS because these files are not binary files. You also have to generate the diamond.amn and UNK files for the plot. Otherwise, the two types of file are not necessary.