[Pw_forum] Convergence issue for C/BN slab

[Biswajit Santra]

Hello,

A few issues I could spot by looking at the input. Should use only 1
k point along the direction of the vacuum. Also, it will be more reasonable
if the number of k points in the direction of celldm(2) is about twice of
that in the direction of celldm(1). The ecutwfc is too large, 60-80 Ry
should be fine.

Best wishes,
Biswajit

Biswajit Santra
Mobile: +1-609-227-9202
http://www.princeton.edu/~bsantra/

On Mon, Feb 20, 2017 at 12:13 PM, Namita Narendra <nnarend at ncsu.edu> wrote:

> Hi,
>
> I am trying to relax a (111) diamond/cubic-BN slab and the total force on
> the atom is not converging. Initially, the scf cycle itself was not
> converging and I needed to introduce smearing with degauss=0.01 to achieve
> scf convergence. Now, the relaxation is not converging and the total force
> on the atom is oscillating. I have tried mixing of 'local-TF', reduced
> mixing_beta, used damped ion dynamics and tried LDA pseudopotential. None
> of this has helped with the convergence issue. Attached below is the input
> file used.
>
>  &CONTROL
> calculation = 'relax' ,
> restart_mode = 'from_scratch' ,
> wf_collect = .true. ,
> outdir = '/share2/nnarend/espresso/c_bn1' ,
> pseudo_dir = '/home/nnarend/pseudo' ,
> prefix = 'C_BN_1' ,
> tstress = .true. ,
> tprnfor = .true. ,
>        forc_conv_thr=1.0D-3,
>        etot_conv_thr=1.0D-4
>  /
>  &SYSTEM
> ibrav = 8,
> celldm(1) = 8.291523,
>        celldm(2)=0.57735,
>        celldm(3)=6,
>        nat = 24,
> ntyp = 3,
> ecutwfc=180.0,
>        occupations='smearing',
>        smearing='cold',
>        degauss=0.01
>
>  /
>  &ELECTRONS
> conv_thr = 1.0d-8,
> mixing_mode = 'plain' ,
> mixing_beta = 0.3 ,
> diagonalization = 'david' ,
>  /
>  &IONS
>  /
> ATOMIC_SPECIES
>    B  10.811  B.pbe-nc.UPF
>    N  14.007  N.pbe-nc.UPF
>    C  12.011 C.pbe-nc.UPF
>
> ATOMIC_POSITIONS alat
> C 0.000000   0.000000   0.000000
> C 0.500000   0.288675   0.000000
> C 0.166667   0.288675   0.117851
> C 0.666667   0.000000   0.117851
> C 0.166667   0.288675   0.471404
> C 0.666667   0.000000   0.471404
> C 0.333333   0.000000   0.589255
> C 0.833333   0.288675   0.589255
> C 0.333333   0.000000   0.942808
> C 0.833333   0.288675   0.942808
> C 0.000000   0.000000   1.060659
> C 0.500000   0.288675   1.060659
> B 0.000000   0.000000   1.414212
> B 0.500000   0.288675   1.414212
> N 0.166667   0.288675   1.532063
> N 0.666667   0.000000   1.532063
> B 0.166667   0.288675   1.885616
> B 0.666667   0.000000   1.885616
> N 0.333333   0.000000   2.003467
> N 0.833333   0.288675   2.003467
> B 0.333333   0.000000   2.357020
> B 0.833333   0.288675   2.357020
> N 0.000000   0.000000   2.474871
> N 0.500000   0.288675   2.474871
>
> K_POINTS automatic
> 8 8 6 0 0 0
>
> Below is the force at the end of each bfgs cycle
>
>      Total force =     0.492043     Total SCF correction =     0.000193
>      Total force =     0.170844     Total SCF correction =     0.000253
>      Total force =     0.049967     Total SCF correction =     0.000085
>      Total force =     0.038773     Total SCF correction =     0.000075
>      Total force =     0.042155     Total SCF correction =     0.000056
>      Total force =     0.046807     Total SCF correction =     0.000072
>      Total force =     0.044401     Total SCF correction =     0.000064
>      Total force =     0.034652     Total SCF correction =     0.000095
>      Total force =     0.033861     Total SCF correction =     0.000065
>      Total force =     0.107334     Total SCF correction =     0.000129
>      Total force =     0.071144     Total SCF correction =     0.000057
>      Total force =     0.053109     Total SCF correction =     0.000077
>      Total force =     0.058897     Total SCF correction =     0.000087
>      Total force =     0.075144     Total SCF correction =     0.000061
>      Total force =     0.109071     Total SCF correction =     0.000025
>      Total force =     0.121561     Total SCF correction =     0.000042
>      Total force =     0.128205     Total SCF correction =     0.000048
>      Total force =     0.138713     Total SCF correction =     0.000070
>
> Thanks,
> Namita
>
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