Density functional theories which are upper bounds to the Hartree-fock limit in one dimension

We begin by constructing the Hartree-Fock density matrix for two model systems, polynomial wavefunctions and the equal-density orbitals. The former yields the generalization of a well-known results for the harmonic oscillator whilst the latter permits the derivation of a density functional theory.     

Phase transitions driven by quasiparticle interactions

After a survey of the solid–liquid transition, driven by phonon–phonon interactions, attention is next focussed on two phase transitions caused by electron–phonon interactions. These are (i) the Barden–Cooper–Schrieffer pure metal superconducting transition and (ii) the original Peierls instability. These have closely similar forms for the respective transition temperatures, both being related to energy gaps. Spin–phonon interactions are then discussed in relation to spin-Peierls materials. Finally, magnon–magnon interactions are treated in the context of the ferromagnetic–paramagnetic transition in the itinerant electron systems Fe, Co and Ni. Heuristic and phenomenological arguments, plus of course experiment, provide the basis for the conclusions drawn here.     

The chemical potential for the inhomogeneous electron liquid in terms of its kinetic and potential parts with special consideration of the surface potential step and BCS-BEC crossover

The chemical potential μ of a many-body system is valuable since it carries fingerprints of phase changes. Here, we summarize results for μ for a three-dimensional electron liquid in terms of average kinetic and potential energies per particle. The difference between μ and the energy per particle is found to be exactly the electrostatic potential step at the surface. We also present calculations for an integrable one-dimensional many-body system with delta function interactions, exhibiting a BCS-BEC crossover. It is shown that in the BCS regime the chemical potential can be expressed solely in terms of the ground-state energy per particle. A brief discussion is also included of the strong coupling BEC limit.     

Optimized geometry of the cluster Gd2O3 and proposed antiferromagnetic alignment of f-electron magnetic moment

There is currently experimental interest in assemblies of Gd2O3 clusters. This has motivated the present study in which a single such cluster in free space is examined quantitatively by spin-density functional theory, with appropriate relativistic corrections incorporated for Gd. First, the nuclear geometry of the cluster is optimized, and it is found to be such that the two Gd atoms lie in a symmetry axis perpendicular to the isosceles triangle formed by the O atoms. Then, a careful study is made of the magnetic arrangement of the localized f-electron moments on the two Gd atoms. The prediction of the present treatment is that the localized spins are aligned antiferromagnetically. An alternative picture using superexchange ideas leads to the same conclusion.     

Exact exchange—correlation potential from low-order density matrices

The local energy equation derived by Dawson and March (1984) following the study of Cohen and Frishberg (1976) involves the low-order density matrices. Using this equation, a formally exact route is laid down by means of which the exchange-correlation potential of density functional theory can be derived in terms of the third- and lower-order density matrices. An integral equation for an approximate exchange potential is obtained, which may be solved iteratively within the Slater-Kohn-Sham scheme. © 1997 John Wiley & Sons, Inc.     

Cryopreservation of Prunus avium L. embryogenic tissues

Embryogenic tissues from wild cherry (Prunus avium L.) were successfully cryopreserved by using a one-step freezing procedure. Cryoprotection consisted of a pretreatment on solid medium with increasing sucrose concentrations (0.25 M for 1 day, 0.5 M for 1 day, 0.75 M for 2 days, and 1.0 M for 3 days), followed by air desiccation to about 20 percent moisture content (fresh weight basis). This method was compared with a pretreatment on solid medium containing 5 percent DMSO and 2 percent proline, followed by immersion in a modified PVS2 cryoprotective solution. Pretreatment on solid medium with increasing concentrations of sucrose led to regrowth of frozen embryogenic tissues, and after 6 weeks of culture, growth was comparable to that of non-dehydrated and non-frozen tissues. By contrast, no regrowth was observed when embryogenic tissues were submitted to the solid/liquid pretreatment with DMSO/proline and a modified PVS2 solution.