Hi all<br>i am claculating cohesive energy of V using pwscf but i got
-8.15 ev/atom against an experimental value of 5.3 ev/atom which is
almost 50% off can anybody say what is going wrong with the
calculation. the method i used is calculate the total energy of a bcc
crystal with 1 atom and deduct the energy of isolated atom from it. the
following input files are for finding the total energy for isolated
atom and the atom in the crystal. Please tell me if my methodology is
wrong.<br>
<br><b>cohesive energy=E per atom (in the crystal)-E per atom (isolated)</b><br><br><b>input file for finding the total energy of an isolated atom</b><br><br>&control<br>calculation = 'scf',<br>restart_mode='from_scratch',<br>

outdir='/home/sai/temp',<br>prefix='vanadium'<br>pseudo_dir='/home/sai/<div id=":19t" class="ii gt">softwares/espresso-4.0.1/pseudo/',<br>tstress = .TRUE.,<br>tprnfor = .TRUE.,<br>/<br>&system<br>
ibrav=1<br>celldm(1)=30,<br>
nat=1,<br>ntyp=1<br>ecutwfc=25,<br>ecutrho=100,<br>occupations='smearing',<br>smearing='mv',<br>degauss=0.010000<br>/<br>&electrons<br>conv_thr=1.D-8,<br>diagonalization='david',<br>  mixing_mode='plain',<br>

mixing_beta= 0.3<br>/<br>ATOMIC_SPECIES<br>V  50.9415  V.pbe-n-van.UPF<br>ATOMIC_POSITIONS (crystal)<br>V       0.00000000      0.00000000      0.00000000<br>K_POINTS {automatic}<br>1 1 1 0 0 0<br><br><b>input file for finding the total energy of the atom in the crystal</b><br>

<br>&control<br>calculation = 'scf',<br>restart_mode='from_scratch',<br>outdir='/home/sai/temp',<br>prefix='vanadium'<br>pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/',<br>

tstress = .TRUE.,<br>tprnfor = .TRUE.,<br>/<br>&system<br>ibrav=3<br>celldm(1)=5.654,<br>nat=1,<br>ntyp=1<br>ecutwfc=25,<br>ecutrho=100,<br>occupations='smearing',<br>smearing='mv',<br>degauss=0.010000<br>

/<br>&electrons<br>conv_thr=1.D-8,<br>diagonalization='david',<br>mixing_mode='plain',<br>mixing_beta= 0.3<br>/<br>ATOMIC_SPECIES<br>V  50.9415  V.pbe-n-van.UPF<br>ATOMIC_POSITIONS (crystal)<br>V       0.00000000      0.00000000      0.00000000<br>

K_POINTS {automatic}<br>8 8 8 0 0 0</div>