[Pw_forum] vdw correction for Bi-layer grahene

[Pang Rui]

In my experience, the London correction on DFT usually overestimates the
interaction so that lead to smaller distance. I suggest you use LDA or
functionals that include vdw corrections inside. 
On Fri, 17 Oct 2014 18:56:05 +0800 (GMT+08:00), plgong
<plgong at theory.issp.ac.cn> wrote:
> Dear pwscf user,
>    Recently, I calculated Bilayer graphene with vdw correction. In
version
>    of 4.3, the parameter of London can be set to 'true'
> and then add vdw correction to Exc. In version of 5.1, more options can
do
> it, such as, 'grimmer-d2', 'dft-d'. However, many tests have been
performed
> but I cannot get the layer-distance (3.34 angstrom in experiment). I
uesd
> GGA-PBE and LDA-PZ with vdw, recepetively. The final results shows small
> distance (3.0 angstrom). I donnot know why leads to the small distance. 
> So, I still tested the Ecut (30Ry-60Ry0) and vaccum (10-20 angstrom),
but
> the problem was the same. 
> The input file is,
> 
> &CONTROL
>                  calculation = 'relax' ,
>                       outdir ='./tmp' ,
>                 restart_mode = 'from_scratch' ,
>                   pseudo_dir ='/home/plgong/pseudo',
>                etot_conv_thr = 1.0e-4 ,
>                forc_conv_thr = 1.0e-3 ,
>                     prefix='graphene',
>  /
>  &SYSTEM
>                        ibrav = 4,
>                            a =2.46
>                            c =10.0
>                          nat = 4,
>                         ntyp = 1,
>                      ecutwfc = 30.D0 ,
>                      ecutrho = 240.0 ,
>                   vdw_corr='grimme-d2'
>                  tot_charge = 0.00,
>                  occupations = 'smearing' ,
>                      degauss = 0.02 ,
>                                          smearing='mv'
> 
>  /
>  &ELECTRONS
>                     conv_thr = 1.D-7 ,
>                      mixing_beta=0.3
>                      mixing_mode='local-TF'
>                 electron_maxstep=300
>  /
>  &IONS
>                 ion_dynamics = 'bfgs' ,
> 
>  /
> ATOMIC_SPECIES
>    C    12.00000   C.pz-rrkjus.UPF
> ATOMIC_POSITIONS {crystal}
> C  0.000000  0.000000  0.500000
> C  0.333333  0.666667  0.500000
> C  0.000000  0.000000  0.834000
> C  0.666667  0.333333  0.834000
> K_POINTS {automatic}
> 30 30 1   0 0 0
> 
> Can anyone help me to solve it? 
> 
> P. L. Gong
> ISSP CAS, HeFei, China
> 
> 
> 
> --
> 
> ====================================================
> Addr: Institute of Solid State Physics, Chinese Academy of 
> Sciences, Hefei, Anhui 230031, China
> Tel: +86-551-65591591(office), 18756086113(cell phone)
> Email: plgong at theory.issp.ac.cn
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-- 
PostDoc
Department of Physics, South University of Science and Technology of China
Shenzhen, Guangdong, PRC, 518500