#NPAR = 2 #NSIM = 2 ENCUT=500 eV NELMIN = 6 ! do a minimum of ten electronic steps EDIFF = 1E-6 ! default accuracy for electronic groundstate EDIFFG = -0.02 ! tolerance for ions NSW = 0 ! 80 ionic steps should do SMASS=0.5 IBRION = 3 POTIM=0.05 ISPIN=2 MAGMOM=1 Back to top Franky Thu Nov 22 2007, 10:27AM I used this INCAR: System = H-Atom Registered Member #629 GGA = 91 Joined: Mon Apr PREC = High 10 03:05PM posts 33 2006, LREAL = .FALSE. ENCUT = 520 ENAUG = 1000 ISPIN = 2 NBANDS = 4 ISMEAR = 0 SIGMA = 0.10 ALGO = Normal NSW = 0 NELM = 60 EDIFF = 1E-7 Kpoint: Automatic 0 Gamma 1 1 1 0 0 0 POSCAR: cubic H 1 10.0 0.0 0.0 0.0 10.0 0.0 0.0 0.0 10.0 1 cartesian 0.0 0.0 0.0 Back to top Franky Thu Nov 22 2007, 10:29AM OUTPUT: FREE ENERGIE OF THE ION-ELECTRON SYSTEM (eV) Registered Member #629 Joined: Mon Apr --------------------------------------------------- 10 2006, free energy TOTEN = -1.120607 eV 03:05PM posts 33 Back to top energy without entropy= -1.120607 energy(sigma->0) = -1.120607 wlyim Sun Nov 25 2007, 06:35PM Dear all, Registered Member #422 I used PAW-PBE for hydrogen (planewave cutoff = 500 eV, charge density Joined: Fri Sep 23 cutoff = 800eV) and the calculated bond dissociation of H2 was 4.54 eV. The 2005, 05:17PM Location: Singapore posts 5 Back to top trick is among the occupation of the atomic species. Try to use \-2\\ = 0.0\and \and \tags. This trick is also crucial to get correct BDE's for other diatomics. Franky Mon Nov 26 2007, 10:09AM Registered Member #629 Using FERWE and FERDO to choose a magnetic groundstate is crucial for certain atoms (see manual). But not for hydrogen since there is only 1 electron. Joined: Mon Apr For H2 it is certainly not an issue because of the unpolarized 10 03:05PM posts 33 2006, groundstate. The H2 / H results (atleast mine) are independent of the ISMEAR tag with an appropriate SIGMA. The crucial point is to closely watch the occ. numbers being: up=1 0 0 ... down=0 0 0 ... for H. ISMEAR = 0 and SIGMA = 0.1 was sufficient to accieve this. And of course to do convergence tests using different ISMEAR and SIGMA. By the way, in order to compare your results to the exp. value (~4.52eV) you have to include zero point vibration of H2. These weaken the theo. bond by ~0.27eV ! Back to top wlyim Tue Nov 27 2007, 02:41PM Registered Hi all, Member #422 I am sorry that my previous reply may be confusing. Anyway, for some cases, Joined: Fri Sep 23 like Cl atom, it is crucial to check the occupation and \ 2005, 05:17PM Location: Singapore posts 5 Referring to Pavel's question, I have tried to reproduce the results. To calculate the dissociation energy of H2, H2 should be calculated using spin-unpolarized, while a spin-polarized calculation for the H atom. It should be mentioned that using spin-polarized calculation for H2 with smearing, it would run into a wrong electronic state (both spin up) and the hydrogen atoms will be separated. I and my co-worker have experienced this before, no matter what kind of basis set and functional. So, one has to check the electronic occupation very carefully when using open-shell calculation for H2. If I understand Pavel correctly, Pavel got a dissociation energy of 0.000x eV, which was a consequence of the open-shell H2 I mentioned.