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["Shtogun, Yaroslav" <yshtogun@cas.usf.edu>]

Dear Abinits users,
 
            I try to study the convergence with respect to number of k 
points, like in lesson 3.

 My crystal is 1D - crystal - (7,0)  carbon nanotubes (please, see my input 
and output in attachment).

 General if we specify many k points the GS energy will be less (from lesson 
3). 

So, in my calculation I specified different ngkpt:

 

ngkpt1 1 1 4      # This is a 1x1x4 grid based on the primitive vectors

ngkpt2 1 1 8

ngkpt3 1 1 12

ngkpt4 1 1 16

ngkpt5 1 1 20

ngkpt6 1 1 24

ngkpt7 1 1 32

ngkpt8 1 1 36

 

    these grids correspond  to next value of k points:

 

     ngfft       250     250      36

      nkpt1        2

      nkpt2        4

      nkpt3        6

      nkpt4        8

      nkpt5       10

      nkpt6       12

      nkpt7       16

      nkpt8       18

 

  in my out file (see attachment) the energy increase when number of k points 
increase - what is wrong, but I don't understand why.

 

    etotal1  -1.5974610701E+02

    etotal2  -1.5974100236E+02

    etotal3  -1.5974076391E+02

    etotal4  -1.5974091974E+02

    etotal5  -1.5974082211E+02

    etotal6  -1.5974086755E+02

    etotal7  -1.5974084928E+02

    etotal8  -1.5974079487E+02

 

  I did one more calculation with next three ngkpt's:  

 

ngkpt1 1 1 4      # This is a 1x1x4 grid based on the primitive vectors

ngkpt2 2 2 4

ngkpt3 4 4 4

 

      nkpt1        2

      nkpt2        2

      nkpt3        8

 

    etotal1  -1.5974610701E+02

    etotal2  -1.5974591557E+02                                                
    

    etotal3  -1.5974599029E+02

 

  in this calculation I got the same dependents, the energy increase with 
number of k points. 

   I really confuse with this results. It seems like 1x1x4 is the lowest grid 
but why the energy increase.

 

   Can somebody explain this strange behavior or some ideas?

 One more question - how to specify right the ngkpt for 1D crystal, is it 
1x1xN or MxMxN?

 

      Thank you in advance

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