[Pw_forum] error on phonon calculation (root not converged)

[Liping YU]

Paolo Giannozzi wrote:

>On Monday 10 April 2006 17:35, Liping YU wrote:
>
>  
>
>>Actually, for 1e-18, though unconvergence message came up
>>in phonon calculation, the dielectric constant I got (see below) 
>>was pretty close to 1.0e-10  in the same 2*2*1 supercell.
>>
>>(2x2x1, tr2_ph=1.0e-18, alpha_mix=0.1)
>>( 222.132924025 0.000000000 0.000000000 )
>>( 0.000000000 222.132924025 0.000000000 )
>>( 0.000000000 0.000000000 6.253206744 )
>>
>>(2x2x1, tr2_ph=1.0e-10, apha_mix=0.1)
>>( 222.139158023 0.000000000 0.000000000 )
>>( 0.000000000 222.139158023 0.000000000 )
>>( 0.000000000 0.000000000 6.262166130 )
>>    
>>
>
>so it is not a problem of convergence. Such large values of the
>dielectric constants mean that the gap is very small.
>
>  
>
>>(1x1x1, tr_ph=1.0e-18, alpha_mix=0.7)
>>( 6.296436141 0.000000000 0.000000000 )
>>( 0.000000000 6.296436141 0.000000000 )
>>( 0.000000000 0.000000000 6.296436141 ).
>>    
>>
>
>If you do a supercell calculation with same atomic positions and 
>equivalent k-point grid as in the original cell, you should get the 
>same Kohn-Sham eigenvalues (refolded into the appropriate 
>k-points) and four time the energy of the original cell. If you don't, 
>please check very carefully your data.
>  
>

1x1x1 cell
Total energy: -275.21362101 ( *4= -1100.85448404 )

k = 0.0000 0.0000 0.0000 ( 1045 PWs) bands (ev):

-45.3707 -22.1221 -21.9779 -21.9779 -21.9779 -7.0142 -5.9530 -5.9530
-4.1784 -4.1784 -4.1784 7.3984 7.3984 7.3984 9.0084 9.0084
9.0084 9.9455 9.9455 9.9455

2x2x1 super cell
Total envergy: -1100.81820918

k = 0.0000 0.0000 0.0000 ( 4189 PWs) bands (ev):

-45.2796 -45.2775 -45.2775 -45.2757 -22.1971 -22.1971 -22.1306 -22.0751
-21.9837 -21.9837 -21.8962 -21.8962 -21.8923 -21.8923 -21.8880 -21.8880
-21.8847 -21.8808 -21.8808 -21.8782 -7.3110 -7.3110 -7.0254 -6.2803
-6.1254 -6.1254 -5.9895 -5.9369 -5.9001 -5.9001 -5.5665 -5.5665
-4.1921 -4.1844 -4.1844 -4.1328 -4.1328 -4.1254 -4.1254 -4.0581
-3.6727 -3.6727 -3.4773 -3.4773 5.2683 5.5759 5.7750 5.7750
5.8965 7.1769 7.1769 7.3059 7.3059 7.3148 7.3148 7.3862
7.3862 7.4078 7.6449 7.6449 7.7312 7.7312 7.7554 7.7554
8.0881 8.0881 8.6134 8.6800 8.6800 8.9788 8.9973 8.9973
9.5426 9.5426 9.5604 9.5604 9.9266 9.9266 9.9563 10.1162

The total energies of them are very close. The largest eigenvalues at gamma
differs from each other about 10.1162- 9.9455 = 0.1707. Is this could be
reseason