> Try to reproduce other properties first (lattice constant, bulk modulus, > etc.) and see if they are reproduced well - that would tell you about > the quality, then you will know whether you need to refine the basis or > maybe even pseudopotential.
Totally agree... > > It is also important how much values and what strain do you impose to > use for fitting. Strain should not exceed 1%. That depends... If you are calculating the bulk modulus using a Murnaghan curve, you can go to 3% without harm to your fit. > > Bulk modulus is not well reproduced in DFT, for elastic constants the > error is even higher. That depends on what you consider as "well-reproduced". 5%-20% is the typical error for this kind of calculations, and IMHO 5% is not bad. Then of course it depends on the system, the energy functional, the basis set you are using... Maybe the problem is that for ZnO one has to take into account the d electrons, either by nonlinear core corrections (which I am not very sure would be enough), either by including them explicitly as semicore states. Anyway, d-electrons can be quite problematic creatures. Are those being taken into account properly in the basis set, or in the pseudopotential? > There is nothing so special in SIESTA to prevent > you from obtaining values of accuracy comparable to other packages with > pseudopotential approach. And again we agree. :) Best regards, Marcos Verissimo Alves > -- 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!
