[Pw_forum] Example7

[Amit Kumar]

   Respected Users,

   I'm very much confused with the Electron-phonon output of Example 7.
   Please check it out:

    1 .  KPOINT  16 16 16 for scf.fit    and   2 2 2 for scf calculation.

    Gaussian Broadening:   0.090 Ry, ngauss=   0
    DOS =  2.674745 states/spin/Ry/Unit Cell at Ef=  8.266810 eV
    lambda( 1)=  0.1373   gamma=   15.97 GHz
    lambda( 2)=  0.1116   gamma=   12.97 GHz
    lambda( 3)=  0.0504   gamma=    6.93 GHz


    Gaussian Broadening:   0.10 Ry, ngauss=   0
    DOS =  2.674314 states/spin/Ry/Unit Cell at Ef=  8.266772 eV
    lambda( 1)=  0.1403   gamma=   16.32 GHz
    lambda( 2)=  0.1132   gamma=   13.16 GHz
    lambda( 3)=  0.0520   gamma=    7.15 GHz



  2.   KPOINT  16 16 16 for scf.fit    and   8 8 8 for scf calculation.

      Gaussian Broadening:   0.090 Ry,       ngauss=   0
      DOS =  2.673746 states/spin/Ry/Unit Cell at Ef=  8.271433 eV
      lambda( 1)=  0.0828   gamma=    8.96 GHz
      lambda( 2)=  0.1720   gamma=   26.90 GHz
      lambda( 3)=  0.1742   gamma=   27.24 GHz


     Gaussian Broadening:   0.10 Ry, ngauss=   0
     DOS =  2.674314 states/spin/Ry/Unit Cell at Ef=  8.266772 eV
     lambda( 1)=  0.0831   gamma=    8.99 GHz
     lambda( 2)=  0.1721   gamma=   26.93 GHz
     lambda( 3)=  0.1740   gamma=   27.22 GHz

     So I thought great I got  convergency so easily.
     lambda( 2)=  0.1720   gamma=   26.90 GHz
     lambda( 3)=  0.1742   gamma=   27.24 GHz

                   and

     lambda( 2)=  0.1721   gamma=   26.93 GHz
     lambda( 3)=  0.1740   gamma=   27.22 GHz

     Very excellent results.

     But. life is not  so simple. Bad luck.
     With even  more K points again results start to become worse instead of
being better.

     Please check it out :


    3.   KPOINT  32 32 32  for scf.fit    and   16 16 16  for scf
calculation.

       Gaussian Broadening:   0.090 Ry,       ngauss=   0
       DOS =  2.675256 states/spin/Ry/Unit Cell at Ef=  8.271367 eV
       lambda( 1)=  0.0799   gamma=    9.12 GHz
       lambda( 2)=  0.1703   gamma=   28.62 GHz
       lambda( 3)=  0.1705   gamma=   28.64 GHz

       Gaussian Broadening:   0.10 Ry,       ngauss=   0
       DOS =  2.674732 states/spin/Ry/Unit Cell at Ef=  8.266803 eV
       lambda( 1)=  0.0799   gamma=    9.12 GHz
       lambda( 2)=  0.1686   gamma=   28.32 GHz
       lambda( 3)=  0.1687   gamma=   28.34 GHz


   4.    KPOINT  64 64 64   for scf.fit    and   32 32 32   for scf
calculation.


        Gaussian Broadening:   0.090 Ry,       ngauss=   0
        DOS =  2.675273 states/spin/Ry/Unit Cell at Ef=  8.271375 eV
        lambda( 1)=  0.0801   gamma=    9.07 GHz
        lambda( 2)=  0.1726   gamma=   28.29 GHz
        lambda( 3)=  0.1726   gamma=   28.29 GHz


        Gaussian Broadening:   0.10 Ry,       ngauss=   0
        DOS =  2.674745 states/spin/Ry/Unit Cell at Ef=  8.266810 eV
        lambda( 1)=  0.0802   gamma=    9.08 GHz
        lambda( 2)=  0.1708   gamma=   27.99 GHz
        lambda( 3)=  0.1708   gamma=   27.99 GHz


         Would anybody tell me the reason,  Why the case (2)    ( for magic
number
         KPOINT  16 16 16 for scf.fit    and   8 8 8 for scf calculation)
is  so kind
         to us?????? How far we will go to get the converged value???
         Where can we stop????
         It's really confusing.

         Looking forward to your help.

         Regards,
         Amit
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