You may want to look at this article: http://prb.aps.org/abstract/PRB/v79/i20/e201309 They calculate electron affinities/ionization potentials, which should be more difficult than what you're trying to do.
Cheers, Lucas On Thu, Apr 12, 2012 at 6:24 AM, Ulrich Biedermann <[email protected]> wrote: > Dear Herbert, > > If the unit cell for the ion is sufficiently large, Siesta prints an estimate > of this interaction energy as Emadel (rather than printing the warning). I > have seen values like 2 eV for a 10x10x10 Angstrom cell. > > For the slab+ion you will always get the warning. > > Your simple approach of using identical unit cells for all calculations may > work (after substracting the Emadel from the ion calculation) in case the > charge remains localized on the ion. However, if it delocalizes onto the > slab or induces shielding charges there is a problem. And to my knowledge no > solution. > > Regards, Ulrich. > > > > ----- Original Message ----- > From: Herbert Fruchtl > [mailto:[email protected]] > To: [email protected] > Sent: Thu, 12 > Apr 2012 11:44:31 +0200 > Subject: [SIESTA-L] Adsorption energy of an ion > > >> Folks, >> >> The manual says not to do it unless you know what you're doing, and since I >> don't, I thought I'd ask... >> >> I want to calculate the adsorption energy of an ion (let's say OH- ) on a >> metal >> surface (let's call it M, denoting a neutral slab of a few layers). The >> straight-forward calculation would be >> >> dE = E(MOH-) - (E(M) + E(OH-)) >> >> Ideally all in the same size of unit cell. There is the problem of BSSE, but >> I >> understand that and know more or less how to handle it. My question concerns >> the >> two charged calculations (MOH- and OH-) and the effect the background charge >> >> that will compensate for the excess electron has on the energy. Is this >> change >> in the Hamiltonian big enough to make the calculated dE meaningless? I have >> seen >> cases where dE (after correction for BSSE, including relaxation energy) came >> out >> positive, which seemed chemically unlikely. >> >> Thanks in advance, >> >> Herbert >> -- >> 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 >> > > --- > Max-Planck-Institut für Eisenforschung GmbH > Max-Planck-Straße 1 > D-40237 Düsseldorf > > Handelsregister B 2533 > Amtsgericht Düsseldorf > > Geschäftsführung > Prof. Dr. Jörg Neugebauer > Prof. Dr. Dierk Raabe > Prof. Dr. Martin Stratmann > Dr. Kai de Weldige > > Ust.-Id.-Nr.: DE 11 93 58 514 > Steuernummer: 105 5891 1000 > ------------------------------------------------- >
