You might want to look at this: https://www.mail-archive.com/[email protected]/msg28550.html
Matthieu Ian Shuttleworth <[email protected]> a écrit : > Hi all > > First, thanks for all the replies. > > My thoughts are that I want vdW for the adsorbate-adsorbate interaction, > the adsorbate-substrate interaction but not for the bulk > substrate-substrate interaction. > > When setting up a surface simulation, you can first determine a bulk > lattice constant. Then, using this lattice constant, you define a slab > which is the truncated bulk and relax the surface layers and add the > adsorbates. So, for a material whose bulk lattice constant is reasonably > well described by non-vdW (e.g. PBEsol) you then overbind if you add vdW > to bulk component of the simulation, and contract the surface lattice > constant as a result. > > I've found that if I get a +1 to +2% bulk lattice parameter overestimation > with PBE, I get an equivalent underestimation if I 'turn on' the vdW > correction. I haven't looked at any other parameters such as formation > energies yet, as I was interested to get some feedback about this lattice > constant problem first, > > Does this sound reasonable? Or am I thinking about the problem incorrectly? > > Again, very kindest thanks for the responses, > > Ian > > > > > > Hi Ian, It is possible with dispersion corrections based on the asymptotic > formula (like XDM or D2, as described by Evren). Why would you want to do > that, though? In general, dispersion improves the description of metals and > ionic solids and, one would guess, surfaces. There was a recent paper by > Perdew and Ruzsinszky on the topic, if memory serves. And I also know for a > fact that, for instance, B86bPBE-XDM reproduces alkali halide and alkaline > earth oxide cubic cell lengths with errors of 0.1 angstrom of less once > vibrational effects are taken into account. > > Best, > > Alberto > > -- > Dr. Alberto Otero de la Roza > Department of Chemistry, > University of British Columbia, Okanagan > Kelowna, British Columbia, Canada V1V 1V7 > > * Ian Shuttleworth <[email protected]> [2017-09-11 16:33:30 +0100]: >> Is it possible to apply vdW forces to only a part of system? >> >> I am thinking of examples where, for example, a vdW adlayer (e.g. benzene) >> sits on a surface, and surface doesn't need vdW corrections. >> >> If I add the vdw_corr toggle (or if I set an appropriate value >> to 'input_dft') I've understood that vdW are applied to the entire system - >> if this is right, how could I make this option more selective? >> >> With thanks >> >> Ian > >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum > > _______________________________________________ > Pw_forum mailing > [email protected]http://pwscf.org/mailman/listinfo/pw_forum _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
