It works...but (sorry Peter) it can be bad science. There are special cases where it is appropriate, but it can also be very inappropriate.
There is a long history of people fixing some atomic positions to bulk positions when performing surface calculations. However, the strain field of any surface decays exponentially in the selvedge layer, and removing this can be very wrong. For instance, there are many known cases where the surface induces a ferroelectric distortion which fixed positions will prevent from happening. The rigorous method is to check that the atomic positions in the center of the slab are "close enough" to those in the bulk. If they are not then either the slab needs to be thicker or there has been a surface induced phase transition. And, fixing positions for a surface *in general does not improve the convergence*. If you are lucky it will, but not in general. The reason (as I have mentioned before) is that the convergence scales with the number and width of the eigenvalue clusters, not the number of variables. If the convergence of Wien2k and other DFT codes scaled with the number of density variables, the methods would be useless! DFT is a useful method because it will typically converge in 10-100 scf iterations because there are only a few eigenvector clusters of the dielectric response (in density only calculations) and the force matrix (with PORT). MSR1a is typically efficient because the number and width of the clusters of the general dielectric response with both density and electronic terms included is smaller than the product of the clusters for the electronic and atomic components. Sorry for being so pedantic...but rigor matters. On Sat, May 19, 2018 at 7:56 AM, Peter Blaha <[email protected]> wrote: > > - How can I lock some atoms in position during structure optimization? > > In case.inM put the 1.0 values of x,y and/or z of the corresponding > atom (line) to 0.0. > > It works well. We do it all the time.... > > > > > Best, > > Lukasz > > > > -- > -------------------------------------------------------------------------- > Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna > Phone: +43-1-58801-165300 FAX: +43-1-58801-165982 > Email: [email protected] WIEN2k: > https://urldefense.proofpoint.com/v2/url?u=http-3A__www. > wien2k.at&d=DwICAg&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_ > T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=HGBSlLfU5SbOh_ > JfodIoRVa6I69Rsj216R2i2idPWPA&s=Z18mJHtLP0OuMpkNbZyk6BppzH7a7i > qaKjSmbAxk0Cw&e= > WWW: > https://urldefense.proofpoint.com/v2/url?u=http-3A__www.imc. > tuwien.ac.at_tc-5Fblaha-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D- > 2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D- > 2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D- > 2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D-2D&d=DwICAg&c= > yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_ > T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=HGBSlLfU5SbOh_ > JfodIoRVa6I69Rsj216R2i2idPWPA&s=GxPbnc8632eZdJgUG2LT9xuLo25j8w > miwf7mi35vykc&e= > > _______________________________________________ > Wien mailing list > [email protected] > https://urldefense.proofpoint.com/v2/url?u=http-3A__zeus. > theochem.tuwien.ac.at_mailman_listinfo_wien&d=DwICAg&c= > yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_ > T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=HGBSlLfU5SbOh_ > JfodIoRVa6I69Rsj216R2i2idPWPA&s=ax2aySwdZVqULGgL- > LOIT7EHit4gKJxeBu2ErcMmvEY&e= > SEARCH the MAILING-LIST at: https://urldefense.proofpoint. > com/v2/url?u=http-3A__www.mail-2Darchive.com_wien- > 40zeus.theochem.tuwien.ac.at_index.html&d=DwICAg&c= > yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_ > T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=HGBSlLfU5SbOh_ > JfodIoRVa6I69Rsj216R2i2idPWPA&s=ke6SIVUCmWlbQaSt9_ > oxTYR55RBkTN_pIRsUznD79B8&e= > -- Professor Laurence Marks "Research is to see what everybody else has seen, and to think what nobody else has thought", Albert Szent-Gyorgi www.numis.northwestern.edu ; Corrosion in 4D: MURI4D.numis.northwestern.edu Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent Co-Editor, Acta Cryst A
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