Thomas: > I don't know of any way of introducing a image charge in the > metallic slab by hand...
well, I would envision a "quick-and-dirty" implementation as follows: determine the position of a "mirror plane", which has to be somewhere closeby to the surface of a real slab, add classical forces to the dynamics from the potential U(d) = -1/2d (in au) where d -- is a normal distance "pseudoanion--mirror plane". Electronic structure calculations are totally unaffected, merely the dynamics is. I can hack verlet code and add these forces directly to the forces() array in the propagation step. The reason I'm looking for the problem---currently my Cl- pseudoanion flies off the surface even if it has a tiny non-zero component of velocity in z direction. The image charge would stop it (which is the physics behind that I'm missing). Of course, I'm totally for the "rigorous" solution of the problem, which, I believe is the constrained DFT with U determined variationally. But you and others already pointed out numerous related issues this solution might bring in to the problem. I shall definitely look at these options but later. Thanks for the discussion anyway! If anyone has other ideas -- please, join the discussion! -- I. -- I. On Wed, Sep 14, 2016 at 4:46 AM, Thomas Brumme <[email protected]> wrote: > Dear Ilya, > > Guiseppe is right and this is also the only way I think you can get > the image charge. You have to use the neutral Cl (i.e. no core > hole), put an extra electron, and force it to stay on Cl. This you > can try with +U (or SIC? or constrained DFT?). Anyway, in this > case you can end up with a dipole in the system and you need to > switch on the dipole correction. And you might get problems with > the homogeneous background if your vacuum is too large and > the area of your slab too small - the electrons could spill into the > minimum which is in the vacuum due to the background. > > I don't know of any way of introducing a image charge in the > metallic slab by hand... > > Thomas > > > On 09/13/2016 10:57 PM, Giuseppe Mattioli wrote: >> Dear Ilya >> I'm afraid there is not too much to add. You can test yourself the >> effect of sa emiempirical application of U by monitorizing the >> occupation of 3s and 3p Cl orbitals in some simple system like a Na >> and a Cl atom far from bond distance or a Cl[H2O]6(-) cluster to see >> when you get Cl(-). A polar solvent/medium stabilizes the excess >> charge and screen the interaction with images (see the role of >> dielectric constant in the old Makov-Payne paper) so that you should >> be able to use lower U values. I've still not published the psII >> calculations and I'm not sure that I will, because it turned out that >> structural results are in a closer agreement with experiment by using >> a GTO framework and COSMO as implicit dielectric environment. >> HTH >> Giuseppe >> >> Quoting Ilya Ryabinkin <[email protected]>: >> >>> 2 Thomas: >>> >>>> Or you can also use the simple dipole correction which was actually >>>> developed for charged (particles on) surfaces, see, e.g., >>> No, I think I wish the opposite: currently my pseudo-anion is neutral, >>> but the *real* one should not be -- and, hence, image charge >>> interaction is missing... I'd like to get it back. >>> >>> Of course, I it is possible and straightforward to keep an extra >>> electron on chlorine and simulate the system with real -1 charge, that >>> all what you've said are relevant and good. >>> >>> So, Giuseppe >>> >>>> I've used a semiempirical U value of 4 eV on the Cl 3p electrons to >>>> keep together the electrons of Cl- in photosystem II. >>> Could you elaborate more on that? Or may be you've published the >>> results -- I could read and reference them. >>> >>> Thanks to all of you, colleagues! >>> >>> -- >>> I. > > -- > Dr. rer. nat. Thomas Brumme > Max Planck Institute for the Structure and Dynamics of Matter > Luruper Chaussee 149 > 22761 Hamburg > > Tel: +49 (0)40 8998 6557 > > email: [email protected] > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum -- ******************************************************* Ilya Ryabinkin Postdoctoral Scholar Physical and Environmental Sciences University of Toronto Scarborough http://www.utsc.utoronto.ca/~aizmaylov/Members.html ******************************************************* _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
