[Pw_forum] problems modeling H2 adsorption on boron doped graphene sheet

[Janet Wong]

Dear QE users,

I am currently in the process of learning how to model hydrogen adsorption on a graphene sheet. So, as a starting point I tried to calculate the adsorption energy of hydrogen on boron doped graphene. However, I am unable to obtain values close to those that were stated in papers with similar DFT calculations. Does anyone have any suggestions as to what I might be doing incorrectly? My calculated value was -0.74 eV (please refer to below for input file used) while other papers stated -0.014 eV. I've tried different orientations for the hydrogen molecule (vertical vs horizontal to the graphene sheet) but my final value doesn't change by much (~0.01eV).

  &control
    prefix='h2ads_BG'
    calculation='relax'
    outdir = './out'
    pseudo_dir = '/scratch/Hydrogen_Adsorption/pseudo/'
    forc_conv_thr=1D-3
 /
 &system
    ibrav=0, nat=34, ntyp=3,
    ecutwfc=25, ecutrho=200
    occupations='smearing', smearing='methfessel-paxton', degauss=0.01
 /
 &electrons
    mixing_mode='local-TF'
 /
 &ions
 /
CELL_PARAMETERS
18.65816237 0.000000000 0.000000000
9.329081185 16.15844260 0.000000000
0.000000000 0.000000000 28.34588983
ATOMIC_SPECIES
 C 12.01  C.pbe-van_bm.UPF
 H 1.001  H.pbe-van_bm.UPF
 B 10.81  B.pbe-n-van.UPF
ATOMIC_POSITIONS angstrom
 C         1.728024        0.709000        0.001000
 C         4.184072        0.709000        0.001000
 C         6.640120        0.709000        0.001000
 C         9.096169        0.709000        0.001000
 C         1.728024        2.127000        0.001000
 C         4.184072        2.127000        0.001000
 C         6.640120        2.127000        0.001000
 C         9.096169        2.127000        0.001000
 C         2.931405        2.793323        0.001000
 C         5.436735        2.793328        0.001000
 C         7.892783        2.793323        0.001000
 C        10.324192        2.793323        0.001000
 C         2.956048        4.254000        0.001000
 C         5.412096        4.254000        0.001000
 B         7.868144        4.254000        0.001000
 H         7.483935        4.254000        1.220000
 H         8.252353        4.254000        1.220000
 C        10.324192        4.254000        0.001000
 C         4.184072        4.963000        0.001000
 C         6.640120        4.963000        0.001000
 C         9.096169        4.963000        0.001000
 C        11.601494        4.963000        0.001000
 C         4.184072        6.381000        0.001000
 C         6.640120        6.381000        0.001000
 C         9.096169        6.381000        0.001000
 C        11.601494        6.381000        0.001000
 C         5.412096        7.090000        0.001000
 C         7.868144        7.090000        0.001000
 C        10.373470        7.090000        0.001000
 C        12.829518        7.090000        0.001000
 C         5.412096        8.508000        0.001000
 C         7.868144        8.508000        0.001000
 C        10.373470        8.508000        0.001000
 C        12.829518        8.508000        0.001000
K_POINTS automatic
5 5 1 1 1 1

Thank you all in advance.

Regards,
Janet Wong
Graduate Student
University of Toronto
Canada
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