scholarly journals AN ATTEMPT AT A RESONATING MEAN-FIELD THEORETICAL DESCRIPTION OF THERMAL BEHAVIOR OF TWO-GAP SUPERCONDUCTIVITY

2013 ◽  
Vol 27 (17) ◽  
pp. 1350079 ◽  
Author(s):  
SEIYA NISHIYAMA ◽  
JOÃO DA PROVIDÊNCIA ◽  
CONSTANÇA PROVIDÊNCIA ◽  
HIROMASA OHNISHI
Keyword(s):  
Thermal Behavior ◽  
Ground State ◽  
Chemical Potential ◽  
Correlation Energy ◽  
Energy Gap ◽  
Mean Field Theory ◽  
Mean Field ◽  
Theoretical Description ◽  
Bogoliubov Theory ◽  
Ground State Correlation

The resonating mean-field theory (Res-MFT) has been applied and shown to effectively describe two-gap superconductivity (SC). Particularly at T = 0 using a suitable chemical potential, the two-gap SC in MgB2 has been well described by the Res-Hartree-Bogoliubov theory (Res-HBT). The Res-HB ground state generated with HB wavefunctions almost exhausts the ground-state correlation energy in all the correlation regimes. In this paper we make an attempt at a Res-MF theoretical description of thermal behavior of the two-gap SC. In an equal energy-gap case we find a new formula leading to a higher critical temperature Tc than the Tc of the usual HB formula.

Ground State Properties of Z = 114 Isotopes in the Relativistic Mean-Field Theory

1997 ◽  
Vol 14 (4) ◽  
pp. 259-262 ◽  
Author(s):  
Ren Zhong-zhou ◽  
Zhu Zhi-yuan ◽  
Cai Yan-huang ◽  
Shen Yao-song ◽  
Zhan Wen-long ◽  
...  
Keyword(s):  
Field Theory ◽  
Ground State ◽  
Mean Field Theory ◽  
Mean Field ◽  
Relativistic Mean Field Theory ◽  
Relativistic Mean Field ◽  
Ground State Properties

VERTEX CORRECTIONS IN THE NUCLEAR SCHWINGER–DYSON FORMALISM

2002 ◽  
Vol 11 (04) ◽  
pp. 321-333 ◽  
Author(s):  
MASAHIRO NAKANO ◽  
HIROYUKI MATSUURA ◽  
TAISUKE NAGASAWA ◽  
KEN-ICHI MAKINO ◽  
NOBUO NODA ◽  
...  
Keyword(s):  
Field Theory ◽  
Correlation Energy ◽  
Mean Field Theory ◽  
Mean Field ◽  
The Other ◽  
Vertex Correction ◽  
Hartree Fock ◽  
Vertex Corrections ◽  
Negative Correlation Energy ◽  
Self Consistent

We develop the Nuclear Schwinger–Dyson (NSD) formalism to include the effects of ladder diagrams by modifying the vertex. In this extension, the NSD equation sums up both ring diagrams and ladder diagrams self-consistently. The results are compared with mean field theory, Hartree Fock and bare-vertex NSD calculations. It is shown that the vertex correction is important from the following viewpoints. First, the vertex correction greatly modifies the meson propagators, and we can avoid the ghost-pole from meson propagators in a self-consistent way. Secondly, it gives a large negative correlation-energy compared with the other calculations; as a result, it gives a softer equation of state which is preferable according to the experimental data.

scholarly journals BEYOND DENSITY FUNCTIONAL THEORY: THE DOMESTICATION OF NONLOCAL POTENTIALS

2004 ◽  
Vol 18 (02n03) ◽  
pp. 73-82 ◽  
Author(s):  
ROBERT K. NESBET
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Correlation Energy ◽  
Mean Field Theory ◽  
Mean Field ◽  
Energy Functional ◽  
Functional Theory ◽  
Large Molecules ◽  
Cellular Method ◽  
Nonlocal Potentials

Due to efficient scaling with electron number N, density functional theory (DFT) is widely used for studies of large molecules and solids. Restriction of an exact mean-field theory to local potential functions has recently been questioned. This review summarizes motivation for extending current DFT to include nonlocal one-electron potentials, and proposes methodology for implementation of the theory. The theoretical model, orbital functional theory (OFT), is shown to be exact in principle for the general N-electron problem. In practice it must depend on a parametrized correlation energy functional. Functionals are proposed suitable for short-range Coulomb-cusp correlation and for long-range polarization response correlation. A linearized variational cellular method (LVCM) is proposed as a common formalism for molecules and solids. Implementation of nonlocal potentials is reduced to independent calculations for each inequivalent atomic cell.

scholarly journals The valence-fluctuating ground state of plutonium

2015 ◽  
Vol 1 (6) ◽  
pp. e1500188 ◽  
Author(s):  
Marc Janoschek ◽  
Pinaki Das ◽  
Bismayan Chakrabarti ◽  
Douglas L. Abernathy ◽  
Mark D. Lumsden ◽  
...  
Keyword(s):  
Ground State ◽  
Degrees Of Freedom ◽  
Mean Field Theory ◽  
Mean Field ◽  
Complex Materials ◽  
Theoretical Understanding ◽  
Electronic Correlations ◽  
Valence Fluctuations ◽  
Electronic Configurations ◽  
Control Complex

A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise because of the competition of localized and itinerant electronic degrees of freedom. Although the respective limits of well-localized or entirely itinerant ground states are well understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and nonbonding configurations. Our study reveals that the ground state of plutonium is governed by valence fluctuations, that is, a quantum mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium’s magnetism but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials.

scholarly journals Thermal resonating Hartree–Bogoliubov theory based on the projection method

2014 ◽  
Vol 28 (20) ◽  
pp. 1450131
Author(s):  
Seiya Nishiyama ◽  
João da Providência ◽  
Hiromasa Ohnishi
Keyword(s):  
Free Energy ◽  
Projection Method ◽  
Continued Fraction ◽  
Mean Field Theory ◽  
Mean Field ◽  
Infinite Matrix ◽  
Bogoliubov Theory ◽  
The Laplace Transform ◽  
Matrix Formula ◽  
Matrix Continued Fraction

We propose a rigorous thermal resonating mean-field theory (Res-MFT). A state is approximated by superposition of multiple MF wavefunctions (WFs) composed of non-orthogonal Hartree–Bogoliubov (HB) WFs. We adopt a Res-HB subspace spanned by Res-HB ground and excited states. A partition function (PF) in a SO (2N) coherent state representation (CS Reps) |g 〉(N: Number of single-particle states) is expressed as Tr (e-βH) = 2N-1∫〈g|e-βH|g〉dg (β = 1/kBT). Introducing a projection operator P to the Res-HB subspace, the PF in the Res-HB subspace is given as Tr (Pe-βH), which is calculated within the Res-HB subspace by using the Laplace transform of e-βH and the projection method. The variation of the Res-HB free energy is made, which leads to a thermal HB density matrix [Formula: see text] expressed in terms of a thermal Res-FB operator [Formula: see text] as [Formula: see text]. A calculation of the PF by an infinite matrix continued fraction (IMCF) is cumbersome and a procedure of tractable optimization is too complicated. Instead, we seek for another possible and more practical way of computing the PF and the Res-HB free energy within the Res-MFT.

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