FixSpin only fixes the total magnetization, making SIESTA very the Fermi levels for up and down spins so that the net spin population will be what you've specified in the parameter. This has nothing to do with the populations on individual atoms. Clearly, trying to impose a fixed spin on each atom would be physically meaningless.
2007/11/28, Marcos Verissimo Alves <[EMAIL PROTECTED]>: > > Eliseo, > > The numbers you are showing for the spins are extracted from some > integration over the densities, or those are the mulliken charges on the > system? I will suppose that those are the numbers that come out after one > or more complete self-consistency cycles; if it is so, it means that your > system "doesn't want to keep" the initial values you have supplied; it > will be more advantageous, energetically, to have the final configuration > of spins. The initial configuration is just a starting guess, but > self-consistency takes over after this. Nothing guarantees that you will > have the final global net spin, or the individual net spins of the atoms, > equal to the initial values after a whole SCF cycle. Actually, you can > constrain the total magnetization of a system in siesta, but I am not sure > if the total magnetization would be constrained over all the scf steps. > > Cheers, > > Marcos > > > > Vous avez écrit / You have written / Lei ha scritto / Você escreveu... > Eliseo Ruiz > > Dear Colleagues, > > > > I am calculating a periodic system with 40 Cu(II) cations in the > > unit cell. I am trying to > > calculate the energy for the different spin distributions. However, > > only in a couple of > > cases I obtain the signs of the spins that I specified in the input > > file. For instance, for one > > of the spin distributions: > > > > ............ > > # Spin defintion > > SpinPolarized T > > FixSpin T > > TotalSpin 8.0 > > %block DM.InitSpin > > 1 +1.0 > > 2 -1.0 > > 3 -1.0 > > 4 +1.0 > > 5 +1.0 > > 6 +1.0 > > 7 -1.0 > > 8 -1.0 > > 9 +1.0 > > 10 +1.0 > > 11 +1.0 > > ............ > > 40 +1.0 > > %endblock DM.InitSpin > > > > the results for the spin density: > > atom up down total > > 1 4.968 -5.401 -.433 > > 2 4.978 -5.411 -.433 > > 3 5.397 -4.948 .449 > > 4 5.406 -4.942 .464 > > 5 5.431 -4.963 .468 > > 6 5.407 -4.962 .445 > > 7 5.415 -4.977 .438 > > 8 4.957 -5.391 -.434 > > 9 4.943 -5.404 -.461 > > 10 5.439 -4.964 .475 > > 12 5.420 -4.987 .433 > > ............ > > > > The total spin is satisfied but not the local spins. I tried several > > options of DM.MixingWeight and > > DM.NumberPulay as well as for ElectronicTemperature but I cannot > > reach the selected spin > > distribution. > > > > best wishes, > > > > Eliseo > > > > > -- > Dr. Marcos Verissimo Alves > Post-Doctoral Fellow > Unité de Physico-Chimie et de Physique des Matériaux (PCPM) > Université Catholique de Louvain > 1 Place Croix du Sud, B-1348 > Louvain-la-Neuve > Belgique > > ------ > > Gort, Klaatu barada nikto. Klaatu barada nikto. Klaatu barada nikto. >
