[Pw_forum] convergence of SCF calculation of C6H8

[Ruibin Liu]

Thank you! In QE, we use supercell to isolate a molecule, right? I don't
understand the differences between isolated and periodic systems in QE.
Anyway, other parameters are as follows:
 &system
    ibrav = 1, celldm(1) =30.0, nat= 14, ntyp= 2,
    ecutwfc = 30.0, ecutrho = 300.0
 /
 &electrons
    diagonalization='david'
    electron_maxstep = 50,
    conv_thr = 1.0e-6
    mixing_beta = 0.1
ATOMIC_SPECIES
 C 12.011   C.blyp-van_ak.UPF
 H 1.008    H.blyp-van_ak.UPF
K_POINTS Gamma

How can I change them?

On Fri, Nov 2, 2012 at 2:32 PM, Axel Kohlmeyer <akohlmey at gmail.com> wrote:

>
>
>
> On Fri, Nov 2, 2012 at 7:22 PM, Ruibin Liu <rainbee1988 at gmail.com> wrote:
>
>> Hi all,
>>
>> I tried to do a scf calculation of C6H8 (CH2CHCHCHCHCH2) with the
>> optimized structure:
>> 6 -0.331356 1.896930 0.000000
>> 6 0.315401 3.090807 0.000000
>> 1 -1.423469 1.885035 0.000000
>> 1 -0.225850 4.033166 0.000000
>> 1 1.402796 3.149961 0.000000
>> 6 0.331356 0.596764 0.000000
>> 6 -0.331356 -0.596764 0.000000
>> 1 1.423645 0.599232 0.000000
>> 6 0.331356 -1.896930 0.000000
>> 1 -1.423645 -0.599232 0.000000
>> 6 -0.315401 -3.090807 0.000000
>> 1 1.423469 -1.885035 0.000000
>> 1 0.225850 -4.033166 0.000000
>> 1 -1.402796 -3.149961 0.000000
>> I have changed the mixing beta several times and also adjusted some
>> coordinates to break symmetry, but the calculation still cannot converge.
>> What else should I pay attention to?
>>
>
> everything. ;-)
>
> there is far to little information (and coordinates don't really help
> much),
> to make a qualified statement. if i would do a wild guess, i'd suggest
> to check if the cell is large enough. atoms might come too close
> due to PBC. is this supposed to be an isolated or periodic system?
>
> axel.
>
>
>
>>
>> Thanks,
>> Ruibin
>> --
>> *Liu, Ruibin*
>> Department of Chemistry
>> Duke University
>> Durham, NC, 27708
>>
>>
>>
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>>
>
>
>
> --
> Dr. Axel Kohlmeyer  akohlmey at gmail.com  http://goo.gl/1wk0
> International Centre for Theoretical Physics, Trieste. Italy.
>
> _______________________________________________
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>



-- 
*Liu, Ruibin*
Department of Chemistry
Duke University
Durham, NC, 27708
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