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Wyświetlanie 1-15 z 41
Tytuł:
Electronic Spaces and Classification of Multielectron States in Multicentre Systems
Autorzy:
Chatterjee, R.
Lulek, T.
Biel, J. K.
Powiązania:
https://bibliotekanauki.pl/articles/1920612.pdf
Data publikacji:
1992-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
02.40.+m
33.10.Cs
71.10.+x
74.60.-w
Opis:
Electronic structure of a crystal within the tight binding model is described in terms of fibre bundle formalism, with the base and fiber being respectively the set of all sites and the single-centre space of electron spinorbitals. It is based on the Weyl's duality between the symmetric group and the unitary group, and paves the way for a Racah-Wigner type of description of electronic structure in multicentre systems.
Źródło:
Acta Physica Polonica A; 1992, 81, 4-5; 467-474
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
About Approximation of Convergence Superoperators in Quantum Perturbation Theory
Autorzy:
Bielińska-Wąż, D.
Paidarova, I.
Durand, Ph.
Powiązania:
https://bibliotekanauki.pl/articles/1964203.pdf
Data publikacji:
1997-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
63.10.+a
71.10.-w
Opis:
Perturbation methods are generally used for solving wave operator equations associated with the determination of effective Hamiltonians. In many cases the standard Rayleigh-Schrodinger and Brillouin-Wigner series either converge slowly or diverge. Therefore it is necessary to modify or to renormalize the standard wave equations. For that purpose derivative and convergence superoperators within the Ralyeigh-Schrodinger and Brillouin-Wigner formalisms were introduced. A new efficient otential is obtained and further application to molecular dynamics is indicated.
Źródło:
Acta Physica Polonica A; 1997, 91, 6; 1061-1068
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Analytic Approximation to Localised ab initio Pseudopotential and Some Applications
Autorzy:
Sarkar, A.
Sen, D.
Powiązania:
https://bibliotekanauki.pl/articles/1964217.pdf
Data publikacji:
1997-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
63.10.+a
71.10.-w
Opis:
The localised version of the density functional based norm-conserving pseudopotential has already been applied to various metallic solids and aggregate state properties with some success. Applications to the study of liquid phonons and to the surface dynamics are specially discussed in the present paper. An analytic fit to the pseudopotential is obtained and further application to molecular dynamics is indicated.
Źródło:
Acta Physica Polonica A; 1997, 91, 6; 1081-1089
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Crossover from BCS to Bose-Einstein in Hubbard Model
Autorzy:
Pedersen, M. H.
Schneider, T.
Beck, H.
Powiązania:
https://bibliotekanauki.pl/articles/1955835.pdf
Data publikacji:
1997-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.10.Fd
74.20.-z
71.10.-w
Opis:
We generalize the standard attractive Hubbard, having an on-site pair creation operator Q$\text{}_{i}$ = a$\text{}_{i↑}$a$\text{}_{i↓}$, to one with n components Q$\text{}_{iα}$ = a$\text{}_{iα↑}$a$\text{}_{iα↓}$, α=1,2,...,n. In the limit n → ∞ we obtain the Ginzburg-Landau functional. On this basis we explore the crossover from weak (BCS) to strong coupling (Bose-Einstein condensation) superconductivity. The associated self-consistent equations for the Ginzburg-Landau parameters are similar to those of the T-matrix approach. The evolution of the band structure with increasing interaction strength is studied and correlated with the behavior of the pair propagator and the transition temperature. We find that the pairing interaction creates a new band which moves downwards in energy as the interaction strength increases and separates into a lower Hubbard band when the interaction strength becomes comparable to the band width. In the strong coupling regime, a third band with small spectral weight is also found in between the lower and upper Hubbard bands.
Źródło:
Acta Physica Polonica A; 1997, 91, 2; 419-422
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Fe Clusters in Fe Intercalated Fullerite
Autorzy:
Sobczak, E.
Żymierska, D.
Byszewski, P.
Traverse, A.
Powiązania:
https://bibliotekanauki.pl/articles/1955842.pdf
Data publikacji:
1997-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.10.Ht
61.46.+w
71.20.Tx
Opis:
The local structure around Fe ions in the C$\text{}_{60}$Fe$\text{}_{2}$ fullerites before and after heat treatment in temperature of 850 K was investigated by means of Fe K edge X-ray absorption near edge structure and extended X-ray absorption near edge structure methods. The X-ray absorption measurements were performed at liquid nitrogen temperature using synchrotron radiation in transmission mode. The X-ray absorption near edge structure and extended X-ray absorption near edge structure studies showed that the heat treatment of the C$\text{}_{60}$Fe$\text{}_{2}$ fullerite at temperature 850 K causing an irreversible transition from monoclinic to fcc structure is accompanied with changes in the state of Fe ions, part of them forms clusters in bcc structure, while others turn to Fe$\text{}^{3+}$ ions bonded to fullerenes.
Źródło:
Acta Physica Polonica A; 1997, 91, 2; 447-450
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On Stability of Frustrated Quantum Magnetic States in Fullerenes
Autorzy:
Koper, A.
Mucha, M.
Powiązania:
https://bibliotekanauki.pl/articles/1964713.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.70.Wz
61.46.+w
71.10.-w
71.27.+a
75.10.Jm
02.50.Ng
02.70.Lq
Opis:
Gutzwiller variational ground states |Φ$\text{}^{G}$⟩ of π electrons, described by single-band half-filling Hubbard model, were determined for the molecules C$\text{}_{60}$ and C$\text{}_{70}$ and their energies and magnetic properties investigated. To construct these states two types of trial functions were used: generalized spin-density wave |Φ$\text{}_{SD}$⟩ and tight-binding wave |Φ$\text{}_{ΤΒ}$⟩. Our results evidently show that the Gutzwiller state |Φ$\text{}_{TΒ}^{G}$⟩ determined by means of function |Φ$\text{}_{ΤΒ}$⟩ has lower energy than the other investigated variational states |Φ$\text{}_{SD}^{G}$⟩. Mean values of the operators in the Gutzwiller states were calculated using Monte Carlo method.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 395-398
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Relation of Gutzwiller Variational State with Matrix Model
Autorzy:
Koper, A.
Mucha, M.
Powiązania:
https://bibliotekanauki.pl/articles/1955829.pdf
Data publikacji:
1997-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
02.70.Lq
02.50.Ng
11.10.-z
71.27.+a
71.10.-w
Opis:
It is shown that mean values of electron operators in variational Gutzwiller state are equal to mean values of corresponding classical quantities calculated by means of a hermitian matrix model. In cases with small number of electrons in the system this property enables exact calculation of the mean values. In case of large number of electrons a simple and effective Monte Carlo method is formulated (within matrix model).
Źródło:
Acta Physica Polonica A; 1997, 91, 2; 391-394
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A New Project for Calculations of e$\text{}^{+}$-e$\text{}^{-}$ Interaction in Real Metals
Autorzy:
Boroński, E.
Powiązania:
https://bibliotekanauki.pl/articles/2007917.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
71.10.-w
71.60.+z
Opis:
A method based on numerical relaxation technique is proposed for solving directly the three-dimensional Euler-Lagrange equation for the density amplitude of conduction electrons in real metals disturbed by the positron. The method has been tested with good results for the positron in an inhomogeneous electron gas. The preliminary calculations of positron screening in lithium give hope for effective applications to real systems.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 461-468
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Non-Local Electron-Positron Enhancement Factors in Solids
Autorzy:
Rubaszek, A.
Szotek, Z.
Temmerman, W.
Powiązania:
https://bibliotekanauki.pl/articles/2008184.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
71.10.-w
71.60.+z
Opis:
Non-local electron-positron correlation effects in solids are studied. The weighted density approximation is applied to calculations of the non-local electron-positron correlation functions. The calculated weighted density approximation electron-positron enhancement factors for the core electrons are compared with those obtained within the local density approximation. Also, differences in the electron-positron enhancement factors due to the s, p, d and f angular momentum channels of the electron charge density are studied. The formalism is applied to ab initio calculations of positron lifetimes in a variety of metals and silicon. The influence of various approximations to the electron-positron interaction on the positron lifetimes is also presented. The weighted density approximation results are compared to those calculated within the local density approximation, the recent generalized gradient approximation and with experimental data.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 652-658
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Kondo-Lattice Metallic and Semiconducting States and Their Instabilities
Autorzy:
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/2011221.pdf
Data publikacji:
2000-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.10.-w
71.10.Fd
Opis:
We review briefly recent results concerning the stability of para-, ferro-, and antiferromagnetic states in the Kondo-lattice limit. Both the macroscopic quantities such as the specific heat and the electrical resistivity, as well as the magnitude of the magnetic moment and the mass enhancement (together with its spin dependence) are discussed.
Źródło:
Acta Physica Polonica A; 2000, 97, 1; 71-79
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Translations for a Spatially Periodic Magnetic Field
Autorzy:
Florek, W.
Powiązania:
https://bibliotekanauki.pl/articles/2013243.pdf
Data publikacji:
2000-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
02.20.-a
73.40.Hm
71.70.Di
71.10.-w
Opis:
It is shown that in the case of a free electron in a spatially periodic magnetic field the concept of magnetic translations operators is still valid and, moreover, these operators can be defined in the same way as for a Bloch electron in a uniform magnetic field. The results can be a useful tool in the investigation of recently observed phenomena in 2D electron gas with spatially modulated density.
Źródło:
Acta Physica Polonica A; 2000, 97, 4; 619-628
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electron-Positron Correlations in Paramagnetic Chromium
Autorzy:
Rubaszek, A.
Szotek, Z.
Temmerman, W. M.
Powiązania:
https://bibliotekanauki.pl/articles/2025045.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
71.10.-w
71.60.+z
Opis:
Several approximations for the electron-positron interaction are applied to study the electron-positron momentum densities of paramagnetic chromium. The non-local and state selective electron-positron correlation functions, evaluated within the weighted density approximation, are used to calculate various positron annihilation characteristics in this system. The weighted density approximation results are compared to the experimental data, and to the corresponding results of the independent particle model, local density approximation, and generalised gradient approximation. Also, the semi-empirical results are used in gaining more physical insight and deriving final conclusions of this work.
Źródło:
Acta Physica Polonica A; 2001, 99, 3-4; 473-477
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Extended Hubbard Model in the Dimer Representation. I. Dimer Hamiltonian in the Large U Limit
Autorzy:
Grabiec, B.
Matlak, M.
Powiązania:
https://bibliotekanauki.pl/articles/2030513.pdf
Data publikacji:
2002-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.-w
71.10.Ca
71.10.Fd
Opis:
We consider the extended Hubbard model for the single cubic lattice and rewrite it in the form of interacting dimers, using the exact solution of the dimer problem. We analytically derive the second quantization form of the dimer Hamiltonian eliminating from the considerations unoccupied dimer energy levels in the large U limit (it is the only assumption). The resulting dimer Hamiltonian written with the use of the Hubbard operators and spin operators contains three terms, visualizing explicitly competing magnetic interactions (ferromagnetic, antiferromagnetic) as a generalization of the t-J model. The presented, nonperturbative method, can in principle be applied to the cluster of any size (e.g. one central atom and z its nearest neighbours). The use of the projection technique can further be applied in the case of a crystal to obtain the second quantization form of the extended Hubbard model for the sc lattice in the large U limit.
Źródło:
Acta Physica Polonica A; 2002, 101, 4; 537-548
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Extended Hubbard Model in the Dimer Representation. II. Lattice Hamiltonian in the Large U Limit
Autorzy:
Grabiec, B.
Matlak, M.
Powiązania:
https://bibliotekanauki.pl/articles/2030514.pdf
Data publikacji:
2002-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.-w
71.10.Ca
71.10.Fd
Opis:
Using the exact decomposition of the sc lattice into a set of interacting dimers (each dimer is described by the extended Hubbard Hamiltonian) and exact solution of the dimer problem (preceding paper) we exactly find the form of the extended Hubbard model in the case of a crystal in the large U limit. We apply a new, nonperturbative approach based on the exact projection procedure onto a dimer subspace occupied by electrons in this limit (it is the only assumption). The resulting Hamiltonian is very complicated and contains a variety of multiple magnetic and nonmagnetic interactions deeply hidden in its original form (site representation). We also present a simplified version of the model to better visualize a mixture of different interactions resulting from this approach.
Źródło:
Acta Physica Polonica A; 2002, 101, 4; 549-557
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Study of the Mott Transition in the Three-Dimensional Hubbard Model
Autorzy:
Mancini, F.
Turkowski, V.
Powiązania:
https://bibliotekanauki.pl/articles/2030509.pdf
Data publikacji:
2002-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.-w
71.10.Fd
71.30.+h
Opis:
The Mott-Hubbard transition in the three-dimensional Hubbard model is studied by means of the composite operator method. Analytical and numerical calculations show the existence of a critical value U$\text{}_{c}$ of the Coulomb interaction which separates paramagnetic insulating and metallic phases. In the composite operator method the ratio U$\text{}_{c}$/W, where W is the band width, has the same value as in the two-dimensional case. The ground state of the Mott insulator is characterized by a local antiferromagnetic order where the electrons keep some mobility, but this latter must be compatible with the local ordering. By analyzing the intersite hopping it is possible to establish that some correlation functions behave as order parameters in the insulating phase.
Źródło:
Acta Physica Polonica A; 2002, 101, 4; 505-523
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 41

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