[Pw_forum] vdw correction for Bi-layer grahene

[plgong]

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



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Email: plgong at theory.issp.ac.cn
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