Thermodynamic potential of the Periodic Anderson Model with the X-boson method: Chain Approximation

The Periodic Anderson Model (PAM) in the $U\to\infty$ limit has been studied in a previous work employing the cumulant expansion with the hybridization as perturbation (M. S. Figueira, M. E. Foglio and G. G. Martinez, Phys. Rev. B \textbf{50}, 17933 (1994)). When the total number of electrons $N_{t}$ is calculated as a function of the chemical potential $\mu$ in the ``Chain Approximation'' (CHA), there are three values of the chemical potential $\mu$ for each $N_{t}$ in a small interval of $N_{t}$ at low $T$ (M. S Figueira, M. E Foglio, Physica A 208 (1994)). We have recently introduced the ``X-boson'' method, inspired in the slave boson technique of Coleman, that solves the problem of non conservation of probability (completeness) in the CHA as well as removing the spurious phase transitions that appear with the slave boson method in the mean field approximation. In the present paper we show that the X-boson method solves also the problem of the multiple roots of $N_{t}(\mu)$ that appear in the CHA.Comment: 13 pages, 6 figures e-mails: [email protected], [email protected], [email protected]

The Cumulant Expansion for the Anderson Lattice with Finite U: The Completeness Problem

``Completeness'' (i.e. probability conservation) is not usually satisfied in the cumulant expansion of the Anderson lattice when a reduced state space is employed for $U\to \infty$. To understand this result, the well known ``Chain'' approximation is first calculated for finite $U$, followed by taking $U\to \infty$. Completeness is recovered by this procedure, but this result hides a serious inconsistency that causes completeness failure in the reduced space calculation. Completeness is satisfied and the inconsistency is removed by choosing an adequate family of diagrams. The main result of this work is that using a reduced space of relevant states is as good as using the whole space.Comment: Latex 22 pages, 6 figures with postscript files attached, accepted for publication in the Int. J. of Mod. Phys. B (1998). Subject field : Strongly Correlated System

Alien Registration- Foglio, Dolres (Biddeford, York County)

https://digitalmaine.com/alien_docs/4651/thumbnail.jp

Kinematic viscosity of unstimulated whole saliva in healthy young adults

To analyze kinematic viscosity and pH of unstimulated whole saliva, evaluate possible variations after sampling, identify any gender differences and detect possible correlations between them

'n Praktiese benadering tot die samestelling van 'n tweerigtingvakwoordeboek met Afrikaans en Italiaans as taalpaar

Deur die tempo van globalisering op handelsgebied ontstaan daar toenemend 'n behoefte aan tweerigtingvakwoordeboeke. Afrikaans is een van die hooftale in Suid-Afrika, en die landbousektor van die land is oorwegend Afrikaanssprekend. Aangesien een van die outeurs Italiaanssprekend is, by vertaling betrokke is en die leemte aan 'n tweerigtingvakwoordeboek Afrikaans en Italiaans ervaar het, is kriteria bepaal vir die samestelling van so 'n vakwoordeboek op die gebied van die landbou-ekonomie tussen Afrikaans, 'n Germaanse taal, en Italiaans, 'n Romaanse taal. In agtereenvolgende afdelings word die algemene kriteria vir die samestelling van so 'n woordeboek uiteengesit. Daarbenewens word voorafgaande werk wat verrig moet word, bespreek, asook die keuring van materiaal. Ten slotte word, aan die hand van gepaste voorbeelde, die leksikografiese beginsels toegepas. 'n Bylaag wat uit twintig lemmas bestaan, dien as voorbeeld van hoe so 'n vakwoordeboek daar behoort uit te sien. Sleutelwoorde: afrikaans, italiaans, leksikografie, terminografie, terminologie, tweerigting, tweetalig, vakleksikografie, vakwoordeboek, woordeboek

X-boson cumulant approach to the periodic Anderson model

The Periodic Anderson Model (PAM) can be studied in the infinite U limit by employing the Hubbard X operators to project out the unwanted states. We have already studied this problem employing the cumulant expansion with the hybridization as perturbation, but the probability conservation of the local states (completeness) is not usually satisfied when partial expansions like the Chain Approximation (CHA) are employed. Here we treat the problem by a technique inspired in the mean field approximation of Coleman's slave-bosons method, and we obtain a description that avoids the unwanted phase transition that appears in the mean-field slave-boson method both when the chemical potential is greater than the localized level Ef at low temperatures (T) and for all parameters at intermediate T.Comment: Submited to Physical Review B 14 pages, 17 eps figures inserted in the tex

Contribution Of The Jahn-teller Effect In The Electronic Raman Scattering In Mgo:co2+

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)A theoretical study of the electronic Raman scattering of MgO with substitutional Co2+ impurities is presented in this paper, and the Jahn-Teller interaction is employed to calculate the line shape. The contribution to the Raman scattering discussed here is different from the phononic contribution studied by other authors. In their calculation, they have implicitly assumed the validity of the Born-Oppenheimer approximation, an assumption that is not valid for the lowest levels of Co2+ in MgO. The electronic Raman intensity is given by an approximate formula that contains the time correlation function of transition operators between the few electronic states of Co2+ that are close to the ground state. To obtain these correlation functions we employ Greens functions, decoupling the equation of motion at a convenient stage of the calculation. Only the normal modes of the complex formed by Co2+ and the six nearest O2- ions have been included in the Jahn-Teller interaction, and they have been expressed as a series of all the lattice phonons. The theoretical phonon spectrum of MgO has also been replaced by a simpler analytical expression that gives its more important features. Most of the parameters that appear in the calculation have been derived from other properties of the system. There is a fairly good agreement between the measured Raman spectrum and the one calculated here. In particular, the relative position of the two 6 '8 and 6 '8 transitions is well explained by the model. The theory also predicts a splitting of the 6 '8 line into a doublet, a fact that is experimentally observed. © 1985 The American Physical Society.32425962603FAPESP; São Paulo Research FoundationFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP