Interface with Wannier90

OpenMX is interfaced with Wannier90 [145] which constructs maximally localized Wannier functions, and calculates physical properties such as Wannier projected DOS and bandstructure, Fermi surface, Berry phase related properties (anomalous Hall conductivity and optical conductivity), and thermoelectric properties. For the calculations, you need to set two keywords as follows:

  Wannier.Func.Calc        on    # on|off, default=off 
  Wannier90.fileout        on    # on|off, default=off

Once you run a job by an input file with the parameter settings shown above, you will see that the job will finish with the following message:

  The input files for Wannier90,

  System.Name.amn
  System.Name.mmn
  System.Name.eig
  System.Name.win

  are successfully generated.

After finishing the calculation, you will obtain the four files listed above. The first three files will be read by 'wannier90.x' of Wannier90, and the last file 'System.Name.win' is an input file to handle the calculation of 'wannier90.x'. The schematic computational flow is shown in Fig. 48. With the overlap matrix 'System.Name.mmn', the projection matrix 'System.Name.amn', and eigenvalues 'System.Name.eig', maximally localized Wannier functions are calculated by using 'wannier90.x'. After getting the maximally localized Wannier functions, by using 'postw90.x' of Wannier90 you can calculate a variety of physical properties such as Berry phase related properties (anomalous Hall conductivity and optical conductivity) and thermoelectric properties. In the file 'System.Name.win' the default setting is for the calculation of optical conductivity as

  berry_task   kubo

By changing the option for the keyword 'berry_task' properly, you may be able to calculate other physical quantities. Some of the options for the keyword are listed below:

  berry_task   kubo     #  optical conductivity 
  berry_task   ahc      #  anomalous Hall conductivity

As for the more details of Wannier90, please refer to the website of Wannier90 [145].

As examples, Figures 49 and 50 show Seebeck coefficient of silicon in the diamond structure and optical conductivity of SrVO$_3$, respectively, calculated by interfacing OpenMX with Wannier90 with the above mentioned scheme. The input files 'Si-Wannier90.dat' and 'SrVO3-Wannier90.dat' can be found in the directory 'work'.

Figure 48: Schematic computational flow for the interface of OpenMX with Wannier90.

Figure 49: (a) Band structure of silicon in the diamond structure, calculated by 8 Wannier orbitals constructed from OpenMX and Wannier90 calculations, and (b) Seebeck coefficient at T=300K estimated from the 8 Wannier bands. The input file used for the OpenMX calculation is 'Si-Wannier90.dat' which is found in the directory 'work'.

Figure 50: (a) Band structure of SrVO$_3$, (b) optical conductivity of SrVO$_3$ calculated by interfacing OpenMX with Wannier90, which is well compared to an experimental optical conductivity in Ref. [147]. The input file used for the OpenMX calculation is 'SrVO3-Wannier90.dat' which is found in the directory 'work'.