Ian, To start with, your input does not represent a slab for siesta, but rather a bulk system. Solution: get cartesian coordinates, specify the input as NotScaledCartesianAng and increase the modulus of the z-vector in the supercell.
Also, 50 Ry will never give you reliable results for anything. Running your system as a slab, before my hard disk died :,(, I saw that the forces were continually increasing as the relaxation proceeded. You will have to check for cutoff convergence, but I would guess 180 Ry would do the job of not allowing your forces to explode. Finally, notice that you will need good sampling of the BZ. And a good basis set as well (SZ is no good at all). Cheers, Marcos > Siesterers > > I am modelling a Cu(001) slab and I want to know how siesta produces a > periodic potential. > > In the below FDF file the unit cell in the x-y direction (defined by the > blocks LatticeVectors and AtomicCoordinatesOrigin) is precisely set to > produce a periodically repeating cell. > > The cell doesnt have the same profile at the boundary values of x and y > but this is necessary to make the structure exactly repeat. > > When the FDF is launched the Cu matrix 'breathes' up and down in the z > direction (the 001 plane spacing first increases then decreases). After a > period the atoms start to displace slightly along the x-y directions. > > My concern then is why the x-y displacements? Is it because of the way the > boundary potentials are evaluated? > > If the boundary along the x=x maximum plane is simply copied from the x=0 > plane (as I suspect) I can understand where imbalance of forces comes > from, and hence why x-y displacements arise. If not, could the origin of > the x-y displacements be rounding error? > > With thanks > > Ian Shuttleworth > > ************************************************************************ > > SystemName cu001 > SystemLabel cu001 > > NumberOfAtoms 75 > NumberOfSpecies 1 > > %block ChemicalSpeciesLabel > 1 29 CU # Species index, atomic number, species label > %endblock ChemicalSpeciesLabel > > PAO.BasisSize SZ > PAO.EnergyShift 300 meV > #NB PAO.EnergyShift value taken from Tests/si64 example - arbitrary for now > > %block Ps.lmax > CU 3 > %endblock Ps.lmax > > #AtomicCoordinatesOrigin block is in Bohr > #1 Bohr = 0.52918 angstroem > > %block AtomicCoordinatesOrigin > 1.205 1.205 9.6376 > %endblock AtomicCoordinatesOrigin > > LatticeConstant 2.55 Ang > %block LatticeVectors > 5.000 0.000 0.000 > 0.000 3.000 0.000 > 0.000 0.000 4.000 > %endblock LatticeVectors > > MeshCutoff 50 Ry > > MaxSCFIterations 50 > DM.MixingWeight 0.3 > DM.NumberPulay 4 > DM.Tolerance 1.d-3 > DM.UseSaveDM > > SolutionMethod diagon > ElectronicTemperature 25 meV > > MD.TypeOfRun cg > MD.NumCGsteps 50 > MD.MaxCGDispl 0.1 Ang > MD.MaxForceTol 0.04 eV/Ang > > AtomicCoordinatesFormat ScaledCartesian > %block AtomicCoordinatesAndAtomicSpecies > 0 0 -1.4142 1 > 1 0 -1.4142 1 > 2 0 -1.4142 1 > 3 0 -1.4142 1 > 4 0 -1.4142 1 > 0 1 -1.4142 1 > 1 1 -1.4142 1 > 2 1 -1.4142 1 > 3 1 -1.4142 1 > 4 1 -1.4142 1 > 0 2 -1.4142 1 > 1 2 -1.4142 1 > 2 2 -1.4142 1 > 3 2 -1.4142 1 > 4 2 -1.4142 1 > 0.5 0.5 -0.7071 1 > 1.5 0.5 -0.7071 1 > 2.5 0.5 -0.7071 1 > 3.5 0.5 -0.7071 1 > 4.5 0.5 -0.7071 1 > 0.5 1.5 -0.7071 1 > 1.5 1.5 -0.7071 1 > 2.5 1.5 -0.7071 1 > 3.5 1.5 -0.7071 1 > 4.5 1.5 -0.7071 1 > 0.5 2.5 -0.7071 1 > 1.5 2.5 -0.7071 1 > 2.5 2.5 -0.7071 1 > 3.5 2.5 -0.7071 1 > 4.5 2.5 -0.7071 1 > 0 0 0 1 > 1 0 0 1 > 2 0 0 1 > 3 0 0 1 > 4 0 0 1 > 0 1 0 1 > 1 1 0 1 > 2 1 0 1 > 3 1 0 1 > 4 1 0 1 > 0 2 0 1 > 1 2 0 1 > 2 2 0 1 > 3 2 0 1 > 4 2 0 1 > 0.5 0.5 0.7071 1 > 1.5 0.5 0.7071 1 > 2.5 0.5 0.7071 1 > 3.5 0.5 0.7071 1 > 4.5 0.5 0.7071 1 > 0.5 1.5 0.7071 1 > 1.5 1.5 0.7071 1 > 2.5 1.5 0.7071 1 > 3.5 1.5 0.7071 1 > 4.5 1.5 0.7071 1 > 0.5 2.5 0.7071 1 > 1.5 2.5 0.7071 1 > 2.5 2.5 0.7071 1 > 3.5 2.5 0.7071 1 > 4.5 2.5 0.7071 1 > 0 0 1.4142 1 > 1 0 1.4142 1 > 2 0 1.4142 1 > 3 0 1.4142 1 > 4 0 1.4142 1 > 0 1 1.4142 1 > 1 1 1.4142 1 > 2 1 1.4142 1 > 3 1 1.4142 1 > 4 1 1.4142 1 > 0 2 1.4142 1 > 1 2 1.4142 1 > 2 2 1.4142 1 > 3 2 1.4142 1 > 4 2 1.4142 1 > %endblock AtomicCoordinatesAndAtomicSpecies > -- Dr. Marcos Verissimo Alves Post-Doctoral Fellow Condensed Matter and Statistical Physics Sector International Centre for Theoretical Physics Trieste, Italy -------- I have become so addicted to vi that I try to exit OpenOffice by typing :wq!
