[Pw_forum] cohesive energy calculation of Zn

[kajal jindal]

Hi all,

I am calculating the cohesive energy of Zn and I am getting a value of
-0.734 eV which is almost 50% of the experimental value of -1.35 eV.Can
anybody plz suggest me what is going wrong with my calculation...I read the
forum regarding it but still unable to resolve my problem..
Following are the input files that i used for the calculation of total
energy of bulk Zn atom in the hexagonal crystal structure and isolated Zn
atom respectively..
/* input file for bulk Zn atom in crystal */
 &control
    calculation='scf',
    restart_mode='from_scratch',
    prefix='bZn'
    wf_collect=.true.,
    pseudo_dir = '/home/kajaljindal/pseudo/',
    outdir= './'
/
 &system
    ibrav = 4, nat= 2, ntyp= 1,celldm(1) = 5.0338, celldm(3) = 1.85829,
    ecutwfc = 60.0,ecutrho=300, occupations ='smearing',smearing='m-v',
    degauss=0.001,starting_magnetization(1)=0.5,nspin=2,nosym=.true.,
/
 &electrons
    mixing_beta = 0.1
    mixing_mode = 'local-TF'
    mixing_ndim = 10
    conv_thr =  1.0e-5
    diagonalization = 'david'
/

ATOMIC_SPECIES
  Zn    65.39      Zn.pbe-van.UPF

ATOMIC_POSITIONS {crystal}
Zn  0.333333  0.666666997  0.249999990
Zn  0.666667  0.333333003  0.750000010

K_POINTS {automatic}
  9 9 6 0 0 0

/* part of the corresponding output file */
     total energy              =    -253.16323313 Ry
     Harris-Foulkes estimate   =    -253.16322516 Ry
     estimated scf accuracy    <       0.00000202 Ry

     The total energy is the sum of the following terms:

     one-electron contribution =    -133.25510851 Ry
     hartree contribution      =      94.29714101 Ry
     xc contribution           =     -37.02058576 Ry
     ewald contribution        =    -177.18467547 Ry
     smearing contrib. (-TS)   =      -0.00000441 Ry

     total magnetization       =     0.00 Bohr mag/cell
     absolute magnetization    =     0.00 Bohr mag/cell

/* input file for isolated atom */
&control
    calculation='scf',
    restart_mode='from_scratch',
    prefix='iZn'
    wf_collect=.true.,
    pseudo_dir = '/home/kajaljindal/pseudo/',
    outdir= './'
/
 &system
    ibrav = 4, nat= 1, ntyp= 1,celldm(1) = 5.0338, celldm(3) = 1.85829,
    ecutwfc = 60.0,ecutrho=300, occupations ='smearing',smearing='m-v',
    degauss=0.001,starting_magnetization(1)=0.5,nspin=2,nosym=.true.,
 /
 &electrons
    mixing_beta = 0.1
    mixing_mode = 'local-TF'
    mixing_ndim = 10
    conv_thr =  1.0e-5
    diagonalization = 'david'
 /
ATOMIC_SPECIES
  Zn    65.39      Zn.pbe-van.UPF

ATOMIC_POSITIONS {crystal}
Zn  0.0  0.0  0.0

K_POINTS {automatic}
  9 9 6 0 0 0

/* part of the corresponding output file */
     total energy              =    -126.55461784 Ry
     Harris-Foulkes estimate   =    -126.55460743 Ry
     estimated scf accuracy    <       0.00000039 Ry

     The total energy is the sum of the following terms:

     one-electron contribution =    -125.24932971 Ry
     hartree contribution      =      73.37661809 Ry
     xc contribution           =     -18.43093183 Ry
     ewald contribution        =     -56.25098076 Ry
     smearing contrib. (-TS)   =       0.00000637 Ry

     total magnetization       =     0.00 Bohr mag/cell
     absolute magnetization    =     0.00 Bohr mag/cell

I deduced twice the total energy for the isolated Zn atom from the energy
for the bulk Zn atom in crystal to obtain the cohesive energy...Plz guide me
where am i going wrong....

Thanks in advance..
sincerely,
Miss Kajal
(UTA)(University of Delhi)
Junior Research Fellow
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