Hi Udayaghiri, Please indicate your affiliation (and preferred name).
My suggestions are: 1) Converge the k-point mesh better for the solid. V is a metal and probably needs more than 8x8x8. 2) Check the energy cutoff convergence on the pseudo-atom. I find that I need more plane waves to describe it than the solid for a given pseudopotential. --William ====================================================================== William Parker Tel : +1 (614) 292-2887 Graduate Research Associate Fax : +1 (614) 292-7557 Ohio State University Department of Physics 191 West Woodruff Avenue email: wparker at mps.ohio-state.edu Columbus, OH 43210-1117 http://www.physics.ohio-state.edu/~wparker U.S.A. Office: 2025 Physics Research Building ====================================================================== On Mon, 31 Aug 2009, udayagiri sai babu wrote: > Hi all > 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. > > *cohesive energy=E per atom (in the crystal)-E per atom (isolated)* > > *input file for finding the total energy of an isolated atom* > > &control > calculation = 'scf', > restart_mode='from_scratch', > outdir='/home/sai/temp', > prefix='vanadium' > pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/', > tstress = .TRUE., > tprnfor = .TRUE., > / > &system > ibrav=1 > celldm(1)=30, > nat=1, > ntyp=1 > ecutwfc=25, > ecutrho=100, > occupations='smearing', > smearing='mv', > degauss=0.010000 > / > &electrons > conv_thr=1.D-8, > diagonalization='david', > mixing_mode='plain', > mixing_beta= 0.3 > / > ATOMIC_SPECIES > V 50.9415 V.pbe-n-van.UPF > ATOMIC_POSITIONS (crystal) > V 0.00000000 0.00000000 0.00000000 > K_POINTS {automatic} > 1 1 1 0 0 0 > > *input file for finding the total energy of the atom in the crystal* > > &control > calculation = 'scf', > restart_mode='from_scratch', > outdir='/home/sai/temp', > prefix='vanadium' > pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/', > tstress = .TRUE., > tprnfor = .TRUE., > / > &system > ibrav=3 > celldm(1)=5.654, > nat=1, > ntyp=1 > ecutwfc=25, > ecutrho=100, > occupations='smearing', > smearing='mv', > degauss=0.010000 > / > &electrons > conv_thr=1.D-8, > diagonalization='david', > mixing_mode='plain', > mixing_beta= 0.3 > / > ATOMIC_SPECIES > V 50.9415 V.pbe-n-van.UPF > ATOMIC_POSITIONS (crystal) > V 0.00000000 0.00000000 0.00000000 > K_POINTS {automatic} > 8 8 8 0 0 0 >
