> Dear Andrei, > > thank you for quick reply. > > I have some experience with AIMPRO which is also based on atom-centered > basis functions, > but it does not have parameters like EnergyShift, EnergySplit, nothing > similar.
Dear Ruslan, exactly as I say: atom-centered basis functions are your free choice, as with a Gaussian orbital code you'd have another system (and different wisdom) to choose the basis, with Slater-type orbitals you'd have yet another, etc. There is no bulletproof rule to construct "the best" basis set. In practical sense, if you are doing Silicon systems: take some of OPTIMIZED basis sets at the Siesta site (via "Pseudos&Bases") produced by Javier Junquera (read related papers, indicated with each basis, in order to make a reasonable choice) and don't worry about it anymore... > What we usually did is we calculated theoretical bulk lattice > constant and then used it in our slab calculations. Yes, that's a good test. > Not like you suggested: vary EnergyShift so that > theoretical and experimental lattice constant coinside. I did not really suggested this, but rather warned against it. > You say that I should care about total energy differences convergence. > Does it mean that the choice of exact EnergyShift > is not so important? > Does the total energy difference only weakly depend on EnergyShift? Now we come into discussion of what is "so important" and what does "weakly depend" mean. Look, this does really, and primarily, depend on which properties you are after. You should test it. But a priori, I'd say, the overall shape and dimension of basis have much more dramatic effect on calculation results than moving around EnergyShift within a given "class" of basis. > You see, my question is practical, how should I choose EnergyShift > so that I could calculate total energy difference correctly? As a rule of thumb (apart from my above suggestion to take, for silicon, a different and well tuned basis): go ahead with Siesta default value, till you'd feel that it does not suit you, for whatever reason. Best regards Andrei
