Spin polarization atoms

Hess, H.F., Kochanski, G.P., Doyle, J.M., Masuhara, N., Kleppner, D. and Greytak, T.J. (1987). Magnetic trapping of spin-polarized atomic hydrogen. Phys. Rev. Lett. 59 672-675. 

Engel, E. and Vosko, S.H. (1993). Accurate optimized-potential-model solutions for spherical spin-polarized atoms Evidence for limitations of the exchange-only local spin-density and generalized-gradient expansions, Phys. Rev. A 47, 2800-2811. 

Let us first discuss a system which is traditional for optical pumping in the Kastler sense [106, 224, 226], namely an optically oriented alkali atom A (see Fig. 1.1) in a noble gas X buffer surrounding. It is important to take into account the fact that in alkali atoms, owing to hyperfine interaction, nuclear spins are also oriented. However, in a mixture of alkali vapor with a noble gas alkali dimers A2 which are in the 1SJ electronic ground state are always present. There exist two basic collisional mechanisms which lead to orientation transfer from the optically oriented (spin-polarized) atom A to the dimer A2 (a) creation and destruction of molecules in triple collisions A + A + X <—> A2 + X (6) exchange atom-dimer reaction... 

The spin-polarized approach also clears up most problems with complex atoms. Of the transition-metal atoms only atomic iron and cobalt have nonintegral numbers of d and s electrons using the Perdew-Zunger [13] local-density functional. From a practical point of view fractional-occupation-number solutions should be avoided at all costs. There appears to be no SCF procedure that will work efficiently for spin-polarized atomic cobalt or iron. Instead one must do several SCF... 

Information on the spin resolved band structure of ferromagnetic materials can directly be obtained from spin resolving photoelectron spectroscopy. Using polarized radiation spin integrating photoemission techniques already enable to have access to magnetic properties. An enhancement of the surface sensitivity can be achieved using neutral excited spin polarized atoms which move towards the sample and are de-excited by tunneling electrons from the surface with a subsequent emission of electrons. 

First, the theoretical study applies to spin-polarized atom-dimer alkali-metal systems, whereas it is not the case for the experiment. A full theoretical treatment should involve the electronic and nuclear spins of the alkali metal atoms as well as couplings between electronic surfaces of different spins. This is beyond the scope of quantum-dynamics calculations at present and will involve significant new code development and massive computational efforts. 

J. Chen, J. B. Krieger, R. O. Esquivel, M. J. Stott, G. J. lafrate. Kohn-Sham effective potentials for spin-polarized atomic systems. Phys. Rev. A, 54(3) (1996) 1910-1921. 

Silvera IF, Walraven JTM. (1986) Spin-polarized atomic H. In Brewer DF (ed.) Progress in Low Temperature Physics. Vol. X. (Elsevier, Amsterdam), pp. 139-370. 

Ahn RMC, van den Eijnde JPHW, Verhaar BJ. (1983) Calculation of nuclear spin relaxation rate for spin-polarized atomic hydrogen. Phys. Rev. B 27 5424-5432. 

Stoof HTC, Janssen AML, Koehnan JMVA, Verhaar BJ. (1989) Decay of spin-polarized atomic hydrogen in the presence of a Bose condensate. Phys. Rev. A 39 3157-3169. 

Grafstrom, S. and Suter, D. (1996). Interaction of spin-polarized atoms with a surface studied by optical-reflection spectroscopy. 

Optimize the structure of acetyl radical using the 6-31G(d) basis set at the HF, MP2, B3LYP and QCISD levels of theory. We chose to perform an Opt Freq calculation at the Flartree-Fock level in order to produce initial force constants for the later optimizations (retrieved from the checkpoint file via OptsReadFC). Compare the predicted spin polarizations (listed as part of the population analysis output) for the carbon and oxygen atoms for the various methods to one another and to the experimental values of 0.7 for the C2 carbon atom and 0.2 for the oxygen atom. Note that for the MP2 and QCISD calculations you will need to include the keyword Density=Current in the job s route section, which specifies that the population analysis be performed using the electron density computed by the current theoretical method (the default is to use the Hartree-Fock density). 

We also plotted the electron spin polarization, by itself (top row) and projected onto the electron density isosurface for the molecules containing the CH2, O and Be substituents (the orientation of the atoms in the plots is indicated at the left) ... 

In a previous work we showed that we could reproduce qualitativlely the LMTO-CPA results for the Fe-Co system within a simple spin polarized canonical band model. The structural properties of the Fe-Co alloy can thus be explained from the filling of the d-band. In that work we presented the results in canonical units and we could of course not do any quantitative comparisons. To proceed that work we have here done calculations based on the virtual crystal approximation (VGA). In this approximation each atom in the alloy has the same surrounding neighbours, it is thus not possible to distinguish between random and ordered alloys, but one may analyze the energy difference between different crystal structures. 

The muffin-tin potential around each atom in the unit cell has been calculated in the framework of the Local-Spin-Density-Approximation using the ASW method. The ASW method uses the atomic sphere approximation (ASA), i.e. for each atom a sphere radius is chosen such that the sum of the volumes of all the overlapping spheres equals the unit cell volume. The calculation yields the expected ferromagnetic coupling between Cr and Ni. From the self-consistent spin polarized DOS, partial and total magnetic moment per formula unit can be computed. The calculated total magnetic moment is 5.2 pg in agreement with the experimental value (5.3 0.1 e calculations presented here have been performed... 

It may be concluded that during the contact time in the competing process for the energy in the various spin systems, the carbon atoms are trying to reach thermal equilibrium with the proton polarization, which is in itself decreasing with a time constant, (Tig, H). In fact the protons undergo spin diffusion and can be treated together, whereas the carbon atoms behave individually. Therefore one implication is that we can also expect to obtain a C-13 spin polarization proportional to the proton polarization. 

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