Peter, Have you tried including BSSE corrections? Check the list email archive, and the literature, for further info on BSSE corrections.
Cheers, Marcos On Fri, Mar 12, 2010 at 3:42 PM, Süle Péter <[email protected]> wrote: > > > Dear SIESTA users, > > I'm trying to determine the cohesive energy > of different compounds and I'am faced with the problem > of overbinding using SIESTA. > Just for an example case I tested simple bcc Fe. > I get Ecohes < -10 eV/atom using standard DZP > basis and various pseudos available in the atm dir > (with and without semi core 3d74s1, pseudo core, normal > 3d64s2 config). The acceptable value would be Ec > -5. eV/atom. > I have no idea how to improve the results. > It could be that further expansion of the basis set to TZP or sg. > could help a bit, although in published papers I found that > DZP is already good for Fe. > The calculation of Ec is as follows: Ec=E(a0)-2*E_atom > or Ec=E(a0)-E(inf), where E(inf) is sg. like a=30. Ang. > It could be I should play with the parameters > PAO.EnergyShift 50 meV > PAO.SplitNorm 0.15 > > MeshCutoff 200.0 Ry > > Best regards, Peter Sule > > > > ---------------------------------------------------- > Dr. Peter Sule > senior research associate > Institue for Technical Physics and Materials Science > (MTA-MFA), Konkoly-Thege M. 29-33, Budapest, Hungary > tel.: (36) 1 392 2222/3605 > fax.: (36) 1 392 22 73 > www.mfa.kfki.hu/~sule / [email protected] > ----------------------------------------------------- > > > > My typical fdf file looks like: > > SystemName bcc fe > SystemLabel fe > > NumberOfAtoms 2 > NumberOfSpecies 1 > > %block ChemicalSpeciesLabel > 1 26 Fe > %endblock ChemicalSpeciesLabel > > #PAO.BasisType nodes > PAO.BasisSize DZP > #PAO.EnergyShift 50 meV > #PAO.SplitNorm 0.15 > > #MeshCutoff 200.0 Ry > > #SpinPolarized T > > MaxSCFIterations 550 > DM.MixingWeight 0.01 > DM.NumberPulay 4 > DM.Tolerance 1.d-4 > #DM.UseSaveDM > > SolutionMethod diagon #orderN > > ElectronicTemperature 3500 K > > Diag.ParallelOverK > > XC.functional GGA > XC.authors PBE > > AtomicCoordinatesFormat Fractional > > %block AtomicCoordinatesAndAtomicSpecies > ck AtomicCoordinatesAndAtomicSpecies > 0.0 0.0 0.0 1 # Fe 1 > 0.5 0.5 0.5 1 # Fe 2 > %endblock AtomicCoordinatesAndAtomicSpecies > > LatticeConstant 2.87 > >
