Dear Andrei, > However, the essence of my previous message: > you do not calculate any SINGLE atom, > you always keep TWO atoms in the unit cell, > but vary the interatomic distance from "very close" > to "infinity" (as the basis atoms of two atoms do not overlap), > then you'll be clean in what regards the BSSE. > 1. Allow the unit cell big enough for that. > 2. Do not forget the magnetism. > This solves some problems, but BSSE is not one of them. To get a BSSE-free PES, one would have to calculate counterpoise correction at every point. My experience with SIESTA is that with the default DZP basis set, BSSE can be fairly large.
Cheers, Herbert > > > > ��2010-04-25 14:30:07��[email protected] �� > >>Dear Haoliang, > >>I think when you compare total energies from Siesta and from Atom, > >>you introduce an unknown error, because they are calculated > >>in quite different way (mesh, basis issues appear in Siesta > >>but not in Atom). It is better to compare comparable values, > >>i.e. total energy of dimer against that of two distant atoms. > >>Define a large enough unit cell to accommodate two separated atoms > >>and, keeping the cell fixed, move the atoms together > >>and trace the energy; hopefully you'll find a minimum at > >>some distance. > >>In doing this, do not forget to make the calculation magnetic > >>and to set the magnetic moments on isolated atoms. > >> > >>Best regards > >> > >>Andrei Postnikov > >> > > -- 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 ------------------------------------------------------------------ University of St Andrews Webmail: https://webmail.st-andrews.ac.uk
