QUANTUM ESPRESSO Wannier

QUANTUM ESPRESSO：wannier

Posted by Xiehua on December 15, 2021

QUANTUM ESPRESSO：Wannier90拟合

从bandfat数据分析，在带隙附近的能带主要由C原子sp2和pz轨道贡献
进行wannier计算的步骤如下：

  1. 用pw.x运行‘scf’计算，使用修改版的PW/src/summary.f90重新编译的pw.x将可以输出能够用于wannier90.x输入文件的结构参数：

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     Begin Write cell and positions for Wannier90.x
 begin unit_cell_cart
 Bohr
     4.8484202   0.0000000   0.0000000
     0.0000000  28.3458919   0.0000000
     0.0000000   0.0000000  28.3458919
 end unit_cell_cart

 begin atoms_cart
 Bohr
     C          -0.0000026  14.1729459  14.1729459
     C           2.3890085  14.1729459  14.1729459
 end atoms_cart
 End Write cell and positions for Wannier90.x

  2. 用pw.x进行’nscf’计算，需要列出所有k点的坐标，和权重，使用kmesh.pl生成。注意修改nbnd，使得其包含要拟合的能带，通过fatband的结果来看需要采用多少条能带。

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    cp scf.in nscf.in

calculation = 'nscf'
nbnd = 22
!K_POINTS{automatic}
!1 1 200 0 0 0

kmesh.pl 1 1 200 >>nscf.in
pw.x <nscf.in>nscf.out

  3. 运行wannier90.x -pp (预处理pre-process，或在输入文件内写postproc_setup = .true.)生成seedname.nnkp。该过程比较快，可以在主节点直接运行。
    使用命令：

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     awk '/Begin Write/,/End Write/' scf.out|awk '/begin unit/,/end atoms/'>>carbyne.win

    • 构建输入文件carbyne.win

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      ! System
begin unit_cell_cart
Ang
 10.000000   0.000000   0.000000
  0.000000  10.000000   0.000000
  0.000000   0.000000   2.56551169
end unit_cell_cart
      
begin atoms_cart
Ang
C       5.0000000000       5.0000000000       0.0000000000
C       5.0000000000       5.0000000000       1.2640744811
end atoms_cart

    • 添加k-points信息 note: dis_win_max的值要根据fatband的结果进行设置，不能随意设置的无限高或者不设置，这样会导致得到的wannier函数很难局域化。Wannier函数局域化的条件要求，(1)wannier函数spread较小，一般每一个wannier函数小于1.0(Ang^2),(2)wannier函数Maximum Im/Re Ratio 的值小，一般应该小于0.001，在wannier函数局域，但是wannier函数虚部比较大时，一般是由于nbnd设置的太少或者太多，当太少时，导致不能projector函数没有包含在所计算的能带中，当太多时，能带中包含了其他的具有相类似性质的投影轨道，导致解纠缠时会很慢收敛，并导致得到解纠缠得到的轨道不合适。在graphene中就是由于nbnd设置的太大导致的这个问题，设置为56时可以得到局域实数的WFs。最好是nbnd的设置，使得在fatband时，正好有相同的投影能带数。（3）Wannier函数拟合得到的能带结构能够与DFT计算得到的能带结构相同,这一条件必须满足。 在画wannier函数时，最好选择cube格式进行输出，采用xcrysden输出的结果采用VESTA画图可能会有问题。

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      echo "mp_grid = 1 1 200">>${seedname}.win
  echo "begin kpoints">>${seedname}.win
  kmesh.pl 1 1 200 wannier >>${seedname}.win
  echo "end kpoints">>${seedname}.win
    • 添加wannier拟合参数
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     !System
 num_wann  = 4
 num_bands = 20
    
 !Projection
 begin projections
 !! Atom-centred px,py orbitals
 !C : px;py
 !! Bond-centred px,py-orbitals
 f=0.5,0.5,0.25:px;py
 f=0.5,0.5,0.75:px;py
 end projections
    
 !Job Control
 exclude_bands : 1-2
 translate_home_cell = .true.
 !restart =
    
 !disentanglement
 dis_win_min  = -10.0
 !dis_win_max  = 12.0
 dis_froz_min = -11.0
 dis_froz_max = -0.5
 dis_num_iter = 1000
 dis_mix_ratio= 0.5
 dis_conv_tol = 1.0E-10
 dis_conv_window = 5
    
 !Wannierise
 num_iter = 10000
 conv_tol = 1.0E-10
 conv_window     = 10
 guiding_centres = .true.
    
 !Post-Processing
 !restart = plot
 wannier_plot = .true.
 wannier_plot_format = cube
 wannier_plot_mode   = crystal
 wannier_plot_supercell = 1 1 3
 translate_home_cell = .true.

 bands_plot = .true.
 bands_num_points = 100
 bands_plot_format = gnuplot
 begin kpoint_path
     M 0.0 0.0 -0.5 G 0.0 0.0 0.0
     G 0.0 0.0  0.0 M 0.0 0.0 0.5
 end kpoint_path

 fermi_surface_plot = .true.
 fermi_surface_num_points = 100
 fermi_energy = -5.262

 write_hr=.true.
 write_rmn=.true.
 write_tb=.true.
 !end plot
    • 运行wannier90.x -pp seedname

    NOTE: 其结果中包含有初始指定的projections函数(以alat为单位)： ! convert wannier center in cartesian coordinates (in unit of alat)

  4. Run pw2wannier90 to compute the overlap between Bloch states and the projections for the starting guess (written in the seedname.mmn and seedname.amn files). 该过程比较慢，最好在计算节点完成。

    pw2wannier90.x < pw2wan.in > pw2wan.out

    输入文件pw2wan.in如下：

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     &inputpp
 outdir = './outdir'
 prefix = 'carbyne'
 seedname = 'carbyne'
 spin_component = 'none'
 write_mmn = .true.
 write_amn = .true.
 write_unk = .true.
 /

    要在后续wannier90.x使用plot画MLWF函数，需要设置write_unk=.true.

    NOTE可能会遇到报错

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     %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 Error in routine  fft_type_set (6):
 there are processes with no planes. Use pencil decomposition (-pd .true.)
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    需要使用mpirun -np $NP pw2wannier90.x <pw2wan.in> pw2wan.out并行计算，并且$NP太大时会导致部分核分配不到平面波，需要适当减小\$NP的值

  5. Run wannier90 to compute the MLWFs.
    mpirun -np 28 wannier90.x seedname
    并在seedname.win中添加plot部分

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    !restart = plot
wannier_plot = .true.
wannier_plot_format = xcrysden
wannier_plot_supercell = 1 1 3
   
bands_plot = .true.
bands_num_points = 100
bands_plot_format = gnuplot
begin kpoint_path
        M 0.0 0.0 -0.5 G 0.0 0.0 0.0
        G 0.0 0.0  0.0 M 0.0 0.0 0.5
end kpoint_path
   
fermi_surface_plot = .true.
fermi_surface_num_points = 100
fermi_energy = -5.262
   
write_hr=.true.
write_rmn=.true.
write_tb=.true.
!end plot

计算得到的wannier插值的能带图如下：
Wannier-band

MLWF如下：
MLWF-1
MLWF-2
MLWF-3
MLWF-4

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