`This "basis set completeness" problem is the basis set superposition error`

`(BSSE), which has been thoroughly studied in molecular calculations. All methods`

`based on atom centred basis sets suffer from it. It basically leads to an`

`artificial attractive force between atoms, because in a more compact system,`

`each atom is described with a more complete basis. In the context of periodic`

`calculations, I would particularly expect it to overestimate surface adsorption`

`energies and underestimate bond lengths.`

Cheers,

Herbert ?????? ????? wrote:

Dear Siesta users, recently Andrei Postnikov wrote a small tutorial on Siesta http://www.home.uni-osnabrueck.de/apostnik/Lectures/SIESTA-tuto.pdf He wrote: "one cannot a priori expect equally good performance of basis overa large range of bond lengths and, say, pressures: as the pressure isvarying, the “completeness”or “variational freedom” of basis in the region of chemically relevant,under a given pressure, bondlengths do vary; consequently the calculated pressure/energy curve mayslightly differ from thatobtained in a “benchmark” FLAPW calculation."A good test would be to compare bulk VASP and Siesta calculations anddeside if calculationin Siesta is accurate enough at some particular pressure. Unfortunatelywe don't have VASP here.My question is (+/- 10%) of the equlibrium lattice constants of Si andGe are Ok for Siesta?Will be Siesta accurate enough to calculate surface energy with an errorof about 1 meV/A2 ?Kind regards Ruslan Zhachuk

-- Herbert Fruchtl Senior Scientific Computing Officer School of Chemistry, School of Mathematics and Statistics University of St Andrews -- The University of St Andrews is a charity registered in Scotland: No SC013532