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Elbio Dagotto - One of the best experts on this subject based on the ideXlab platform.
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magnetic phase diagram of a five orbital hubbard model in the real space hartree Fock Approximation varying the electronic density
Physical Review B, 2014Co-Authors: Qinlong Luo, Elbio DagottoAbstract:Using the real-space Hartree-Fock Approximation, the magnetic phase diagram of a five-orbital Hubbard model for the iron-based superconductors is studied varying the electronic density $n$ in the range from five to seven electrons per transition metal atom. The Hubbard interaction $U$ is also varied, at a fixed Hund coupling $J/U=0.25$. Several qualitative trends and a variety of competing magnetic states are observed. At $n=5$, a robust G-type antiferromagnetic insulator is found, in agreement with experimental results for BaMn${}_{2}$As${}_{2}$. As $n$ increases away from 5, magnetic states with an increasing number of nearest-neighbors ferromagnetic links become energetically stable. This includes the well-known C-type antiferromagnetic state at $n=6$, the E-phase known to exist in FeTe, and also a variety of novel states not found yet experimentally, some of them involving blocks of ferromagnetically oriented spins. Regions of phase separation, as in Mn oxides, have also been detected. Comparison to previous theoretical investigations indicate that these qualitative trends may be generic characteristics of phase diagrams of multi-orbital Hubbard models.
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magnetic phase diagram of a five orbital hubbard model in the real space hartree Fock Approximation varying the electronic density
Physical Review B, 2014Co-Authors: Qinlong Luo, Elbio DagottoAbstract:Using the real-space Hartree Fock Approximation, the magnetic phase diagram of a five-orbital Hubbard model for the iron-based superconductors is studied varying the electronic density $n$ in the range from 5 to 7 electrons per transition metal atom. The Hubbard interaction $U$ is also varied, at a fixed Hund coupling $J/U=0.25$. Several qualitative trends and a variety of competing magnetic states are observed. At $n$=5, a robust G-type antiferromagnetic insulator is found, in agreement with experimental results for BaMn$_2$As$_2$. As $n$ increases away from 5, magnetic states with an increasing number of nearest-neighbors ferromagnetic links become energetically stable. This includes the well-known C-type antiferromagnetic state at $n$=6, the E-phase known to exist in FeTe, and also a variety of novel states not found yet experimentally, some of them involving blocks of ferromagnetically oriented spins. Regions of phase separation, as in Mn-oxides, have also been detected. Comparison with previous theoretical investigations indicate that these qualitative trends may be generic characteristics of phase diagrams of multiorbital Hubbard models.
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magnetic state of k0 8fe1 6se2 from a five orbital hubbard model in the hartree Fock Approximation
Physical Review B, 2011Co-Authors: Qinlong Luo, Andrew Nicholson, Jose Riera, Daoxin Yao, Adriana Moreo, Elbio DagottoAbstract:Motivated by the recent discovery of Fe-based superconductors close to an antiferromagnetic insulator in the experimental phase diagram, here the five-orbital Hubbard model (without lattice distortions) is studied using the real-space Hartree-Fock Approximation, employing a 10 10 Fe cluster with Fe vacancies in a5 5 pattern. Varying the Hubbard and Hund couplings, and at electronic density n = 6.0, the phase diagram contains an insulating state with the same spin pattern as observed experimentally, involving 2 2 ferromagnetic plaquettes coupled with one another antiferromagnetically. The presence of local ferromagnetic tendencies is in qualitative agreement with Lanczos results for the three-orbital model also reported here. The magnetic moment 3 B /Fe is in good agreement with experiments. Several other phases are also stabilized in the phase diagram, in agreement with recent calculations using phenomenological models.
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magnetic state of k 0 8 fe 1 6 se 2 from a five orbital hubbard model in the hartree Fock Approximation
Physical Review B, 2011Co-Authors: Qinlong Luo, Andrew Nicholson, Jose Riera, Daoxin Yao, Adriana Moreo, Elbio DagottoAbstract:Motivated by the recent discovery of Fe-based superconductors close to an antiferromagnetic insulator in the experimental phase diagram, here the five-orbital Hubbard model (without lattice distortions) is studied using the real-space Hartree-Fock Approximation, employing a $10\ifmmode\times\else\texttimes\fi{}10$ Fe cluster with Fe vacancies in a $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}$ pattern. Varying the Hubbard and Hund couplings, and at electronic density $n=6.0$, the phase diagram contains an insulating state with the same spin pattern as observed experimentally, involving $2\ifmmode\times\else\texttimes\fi{}2$ ferromagnetic plaquettes coupled with one another antiferromagnetically. The presence of local ferromagnetic tendencies is in qualitative agreement with Lanczos results for the three-orbital model also reported here. The magnetic moment $\ensuremath{\sim}$3${\ensuremath{\mu}}_{B}/$Fe is in good agreement with experiments. Several other phases are also stabilized in the phase diagram, in agreement with recent calculations using phenomenological models.
Qinlong Luo - One of the best experts on this subject based on the ideXlab platform.
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magnetic phase diagram of a five orbital hubbard model in the real space hartree Fock Approximation varying the electronic density
Physical Review B, 2014Co-Authors: Qinlong Luo, Elbio DagottoAbstract:Using the real-space Hartree-Fock Approximation, the magnetic phase diagram of a five-orbital Hubbard model for the iron-based superconductors is studied varying the electronic density $n$ in the range from five to seven electrons per transition metal atom. The Hubbard interaction $U$ is also varied, at a fixed Hund coupling $J/U=0.25$. Several qualitative trends and a variety of competing magnetic states are observed. At $n=5$, a robust G-type antiferromagnetic insulator is found, in agreement with experimental results for BaMn${}_{2}$As${}_{2}$. As $n$ increases away from 5, magnetic states with an increasing number of nearest-neighbors ferromagnetic links become energetically stable. This includes the well-known C-type antiferromagnetic state at $n=6$, the E-phase known to exist in FeTe, and also a variety of novel states not found yet experimentally, some of them involving blocks of ferromagnetically oriented spins. Regions of phase separation, as in Mn oxides, have also been detected. Comparison to previous theoretical investigations indicate that these qualitative trends may be generic characteristics of phase diagrams of multi-orbital Hubbard models.
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magnetic phase diagram of a five orbital hubbard model in the real space hartree Fock Approximation varying the electronic density
Physical Review B, 2014Co-Authors: Qinlong Luo, Elbio DagottoAbstract:Using the real-space Hartree Fock Approximation, the magnetic phase diagram of a five-orbital Hubbard model for the iron-based superconductors is studied varying the electronic density $n$ in the range from 5 to 7 electrons per transition metal atom. The Hubbard interaction $U$ is also varied, at a fixed Hund coupling $J/U=0.25$. Several qualitative trends and a variety of competing magnetic states are observed. At $n$=5, a robust G-type antiferromagnetic insulator is found, in agreement with experimental results for BaMn$_2$As$_2$. As $n$ increases away from 5, magnetic states with an increasing number of nearest-neighbors ferromagnetic links become energetically stable. This includes the well-known C-type antiferromagnetic state at $n$=6, the E-phase known to exist in FeTe, and also a variety of novel states not found yet experimentally, some of them involving blocks of ferromagnetically oriented spins. Regions of phase separation, as in Mn-oxides, have also been detected. Comparison with previous theoretical investigations indicate that these qualitative trends may be generic characteristics of phase diagrams of multiorbital Hubbard models.
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magnetic state of k0 8fe1 6se2 from a five orbital hubbard model in the hartree Fock Approximation
Physical Review B, 2011Co-Authors: Qinlong Luo, Andrew Nicholson, Jose Riera, Daoxin Yao, Adriana Moreo, Elbio DagottoAbstract:Motivated by the recent discovery of Fe-based superconductors close to an antiferromagnetic insulator in the experimental phase diagram, here the five-orbital Hubbard model (without lattice distortions) is studied using the real-space Hartree-Fock Approximation, employing a 10 10 Fe cluster with Fe vacancies in a5 5 pattern. Varying the Hubbard and Hund couplings, and at electronic density n = 6.0, the phase diagram contains an insulating state with the same spin pattern as observed experimentally, involving 2 2 ferromagnetic plaquettes coupled with one another antiferromagnetically. The presence of local ferromagnetic tendencies is in qualitative agreement with Lanczos results for the three-orbital model also reported here. The magnetic moment 3 B /Fe is in good agreement with experiments. Several other phases are also stabilized in the phase diagram, in agreement with recent calculations using phenomenological models.
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magnetic state of k 0 8 fe 1 6 se 2 from a five orbital hubbard model in the hartree Fock Approximation
Physical Review B, 2011Co-Authors: Qinlong Luo, Andrew Nicholson, Jose Riera, Daoxin Yao, Adriana Moreo, Elbio DagottoAbstract:Motivated by the recent discovery of Fe-based superconductors close to an antiferromagnetic insulator in the experimental phase diagram, here the five-orbital Hubbard model (without lattice distortions) is studied using the real-space Hartree-Fock Approximation, employing a $10\ifmmode\times\else\texttimes\fi{}10$ Fe cluster with Fe vacancies in a $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}$ pattern. Varying the Hubbard and Hund couplings, and at electronic density $n=6.0$, the phase diagram contains an insulating state with the same spin pattern as observed experimentally, involving $2\ifmmode\times\else\texttimes\fi{}2$ ferromagnetic plaquettes coupled with one another antiferromagnetically. The presence of local ferromagnetic tendencies is in qualitative agreement with Lanczos results for the three-orbital model also reported here. The magnetic moment $\ensuremath{\sim}$3${\ensuremath{\mu}}_{B}/$Fe is in good agreement with experiments. Several other phases are also stabilized in the phase diagram, in agreement with recent calculations using phenomenological models.
Patrick Norman - One of the best experts on this subject based on the ideXlab platform.
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first order excited state properties in the four component hartree Fock Approximation the excited state electric dipole moments in csag and csau
Journal of Chemical Physics, 2007Co-Authors: Erik I Tellgren, Johan Henriksson, Patrick NormanAbstract:An implementation of the second-order residue of the quadratic response function is presented in the four-component Hartree-Fock Approximation, and the calculation of first-order properties of elec ...
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two photon absorption in the relativistic four component hartree Fock Approximation
Journal of Chemical Physics, 2005Co-Authors: Johan Henriksson, Patrick Norman, Hans Jorgen Aa JensenAbstract:A first implementation of the single residue of the quadratic response function in the four-component Hartree–Fock Approximation is presented. The implementation is based on a Kramers paired molecular orbital basis and takes full advantage of time and spatial symmetry reductions in a quaternion formulation—in analogy with the previous work on the quadratic response function [J. Chem. Phys. 121, 6145 (2004)]. Sample calculations are given in terms of the monochromatic and coherent two-photon absorption cross sections in the noble gases. The relativistic two-photon selection rule ΔJ={0,±2} allows for nonrelativistically spin-forbidden transitions, and, even in neon, strong two-photon absorption is shown to occur for the XS01→2P23 transition. It is argued that relevant comparisons between nonrelativistic and relativistic calculations must be performed at the level of integrated absorption cross sections.
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quadratic response functions in the time dependent four component hartree Fock Approximation
Journal of Chemical Physics, 2004Co-Authors: Patrick Norman, Hans Jorgen Aa JensenAbstract:The second-order response function has been implemented in the time-dependent four-component Hartree-Fock Approximation. The implementation is atomic orbital direct and formulated in terms of Fock-type matrices. It employs a quaternion symmetry scheme that provides maximum computational efficiency with consideration made to time-reversal and spatial symmetries. Calculations are presented for the electric dipole first-order hyperpolarizabilities of CsAg and CsAu in the second-harmonic generation optical process β(−2ω;ω,ω). It is shown that relativistic corrections to property values are substantial in these cases—the orientationally averaged hyperpolarizabilities in the static limit β(0;0,0) are overestimated in nonrelativistic calculations by 18% and 66% for CsAg and CsAu, respectively. The dispersion displays anomalies in the band gap region due to one- and two-photon resonances with nonrelativistically spin-forbidden states. Although weakly absorbing these states inflict divergences in the quadratic re...
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relativistic effects on linear and nonlinear polarizabilities studied by effective core potential douglas kroll and dirac hartree Fock response theory
Journal of Chemical Physics, 2002Co-Authors: Patrick Norman, Hans Jorgen Aa Jensen, Bernd Schimmelpfennig, Kenneth Ruud, Hans AgrenAbstract:Relativistic calculations of electric dipole moments, linear polarizabilities, and first- and second-order hyperpolarizabilities have been carried out for the isovalent group VI dihydrides (O–Po) and group VII monohydrides (F–At) at three different levels: the time-dependent Dirac–Hartree–Fock Approximation, the time-dependent Hartree–Fock Approximation with a Douglas–Kroll transformed one-component Hamiltonian, and the time-dependent Hartree–Fock Approximation with effective-core potentials. These calculations are compared with nonrelativistic time-dependent Hartree–Fock results in order to elucidate the role of relativistic effects on these properties and to investigate the extent to which the Douglas–Kroll approach and the effective-core potentials—both of which neglect spin-dependent terms but are computationally less demanding—are able to reproduce the 4-component Dirac–Hartree–Fock results. The results show that qualitatively correct relativistic corrections in most cases can be obtained with the more approximative methods, but that a quantitative agreement with 4-component calculations is often not obtained.
Hans Jorgen Aa Jensen - One of the best experts on this subject based on the ideXlab platform.
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two photon absorption in the relativistic four component hartree Fock Approximation
Journal of Chemical Physics, 2005Co-Authors: Johan Henriksson, Patrick Norman, Hans Jorgen Aa JensenAbstract:A first implementation of the single residue of the quadratic response function in the four-component Hartree–Fock Approximation is presented. The implementation is based on a Kramers paired molecular orbital basis and takes full advantage of time and spatial symmetry reductions in a quaternion formulation—in analogy with the previous work on the quadratic response function [J. Chem. Phys. 121, 6145 (2004)]. Sample calculations are given in terms of the monochromatic and coherent two-photon absorption cross sections in the noble gases. The relativistic two-photon selection rule ΔJ={0,±2} allows for nonrelativistically spin-forbidden transitions, and, even in neon, strong two-photon absorption is shown to occur for the XS01→2P23 transition. It is argued that relevant comparisons between nonrelativistic and relativistic calculations must be performed at the level of integrated absorption cross sections.
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quadratic response functions in the time dependent four component hartree Fock Approximation
Journal of Chemical Physics, 2004Co-Authors: Patrick Norman, Hans Jorgen Aa JensenAbstract:The second-order response function has been implemented in the time-dependent four-component Hartree-Fock Approximation. The implementation is atomic orbital direct and formulated in terms of Fock-type matrices. It employs a quaternion symmetry scheme that provides maximum computational efficiency with consideration made to time-reversal and spatial symmetries. Calculations are presented for the electric dipole first-order hyperpolarizabilities of CsAg and CsAu in the second-harmonic generation optical process β(−2ω;ω,ω). It is shown that relativistic corrections to property values are substantial in these cases—the orientationally averaged hyperpolarizabilities in the static limit β(0;0,0) are overestimated in nonrelativistic calculations by 18% and 66% for CsAg and CsAu, respectively. The dispersion displays anomalies in the band gap region due to one- and two-photon resonances with nonrelativistically spin-forbidden states. Although weakly absorbing these states inflict divergences in the quadratic re...
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relativistic effects on linear and nonlinear polarizabilities studied by effective core potential douglas kroll and dirac hartree Fock response theory
Journal of Chemical Physics, 2002Co-Authors: Patrick Norman, Hans Jorgen Aa Jensen, Bernd Schimmelpfennig, Kenneth Ruud, Hans AgrenAbstract:Relativistic calculations of electric dipole moments, linear polarizabilities, and first- and second-order hyperpolarizabilities have been carried out for the isovalent group VI dihydrides (O–Po) and group VII monohydrides (F–At) at three different levels: the time-dependent Dirac–Hartree–Fock Approximation, the time-dependent Hartree–Fock Approximation with a Douglas–Kroll transformed one-component Hamiltonian, and the time-dependent Hartree–Fock Approximation with effective-core potentials. These calculations are compared with nonrelativistic time-dependent Hartree–Fock results in order to elucidate the role of relativistic effects on these properties and to investigate the extent to which the Douglas–Kroll approach and the effective-core potentials—both of which neglect spin-dependent terms but are computationally less demanding—are able to reproduce the 4-component Dirac–Hartree–Fock results. The results show that qualitatively correct relativistic corrections in most cases can be obtained with the more approximative methods, but that a quantitative agreement with 4-component calculations is often not obtained.
Koichi Saito - One of the best experts on this subject based on the ideXlab platform.
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decomposition of nuclear symmetry energy based on lorentz covariant nucleon self energies in relativistic hartree Fock Approximation
Physics Letters B, 2020Co-Authors: Tsuyoshi Miyatsu, Myungki Cheoun, Chikako Ishizuka, K S Kim, Tomoyuki Maruyama, Koichi SaitoAbstract:Abstract Using the Lorentz-covariant decomposition of nucleon self-energies based on the Hugenholtz–Van Hove theorem, we study the effect of Fock terms on the nuclear symmetry energy and its slope parameter within relativistic Hartree-Fock Approximation. It is found that the exchange contribution suppresses the nuclear symmetry energy and prevents the slope parameter from increasing monotonically at high densities. Furthermore, not only the isovector-vector (ρ) meson but also the isoscalar mesons ( σ , ω ) and pion give significant influence on the potential term of nuclear symmetry energy through the exchange diagrams.
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equation of state for neutron stars with hyperons and quarks in the relativistic hartree Fock Approximation
The Astrophysical Journal, 2015Co-Authors: Tsuyoshi Miyatsu, Myungki Cheoun, Koichi SaitoAbstract:We construct the equation of state (EoS) for neutron stars explicitly including hyperons and quarks. Using the quark-meson coupling model with relativistic Hartree-Fock Approximation, the EoS for hadronic matter is derived by taking into account the strange ($\sigma^{\ast}$ and $\phi$) mesons as well as the light non-strange ($\sigma$, $\omega$, $\vec{\pi}$ and $\vec{\rho}$) mesons. Relevant coupling constants are determined to reproduce the experimental data of nuclear matter and hypernuclei in SU(3) flavor symmetry. For quark matter, we employ the MIT bag model with one-gluon-exchange interaction, and Gibbs criteria for chemical equilibrium in the phase transition from hadrons to quarks. We find that the strange vector ($\phi$) meson and the Fock contribution make the hadronic EoS stiff, and that the maximum mass of a neutron star can be consistent with the observed mass of heavy neutron stars even if the coexistence of hadrons and quarks takes place in the core. However, in the present calculation the transition to pure quark matter does not occur in stable neutron stars. Furthermore, the lower bound of the critical chemical potential of the quark-hadron transition at zero temperature turns out to be around 1.5 GeV in order to be consistent with the recent observed neutron star data.
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equation of state for neutron stars with hyperons and quarks in the relativistic hartree Fock Approximation
The Astrophysical Journal, 2015Co-Authors: Tsuyoshi Miyatsu, Myungki Cheoun, Koichi SaitoAbstract:We construct the equation of state (EoS) for neutron stars explicitly including hyperons and quarks. Using the quark–meson coupling model with the relativistic Hartree–Fock Approximation, the EoS for hadronic matter is derived by taking into account the strange (σ* and ϕ) mesons as well as the light non-strange (σ, ω, ${\boldsymbol{\pi }}$, and ${\boldsymbol{\rho }}$) mesons. Relevant coupling constants are determined to reproduce the experimental data of nuclear matter and hypernuclei in SU(3) flavor symmetry. For quark matter, we employ the MIT bag model with a one-gluon-exchange interaction, and Gibbs criteria for chemical equilibrium in the phase transition from hadrons to quarks. We find that the strange vector (ϕ) meson and the Fock contribution make the hadronic EoS stiff, and that the maximum mass of a neutron star can be consistent with the observed mass of heavy neutron stars even if the coexistence of hadrons and quarks takes place in the core. However, in the present calculation, the transition to pure quark matter does not occur in stable neutron stars. Furthermore, the lower bound of the critical chemical potential of the quark–hadron transition at zero temperature turns out to be around 1.5 GeV in order to be consistent with the recent observed neutron-star data.
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equation of state for neutron stars with hyperons and quarks in relativistic hartree Fock Approximation
arXiv: Nuclear Theory, 2015Co-Authors: Tsuyoshi Miyatsu, Myungki Cheoun, Koichi SaitoAbstract:We construct the equation of state (EoS) for neutron stars explicitly including hyperons and quarks. Using the quark-meson coupling model with relativistic Hartree-Fock Approximation, the EoS for hadronic matter is derived by taking into account the strange ($\sigma^{\ast}$ and $\phi$) mesons as well as the light non-strange ($\sigma$, $\omega$, $\vec{\pi}$ and $\vec{\rho}$) mesons. Relevant coupling constants are determined to reproduce the experimental data of nuclear matter and hypernuclei in SU(3) flavor symmetry. For quark matter, we employ the MIT bag model with one-gluon-exchange interaction, and Gibbs criteria for chemical equilibrium in the phase transition from hadrons to quarks. We find that the strange vector ($\phi$) meson and the Fock contribution make the hadronic EoS stiff, and that the maximum mass of a neutron star can be consistent with the observed mass of heavy neutron stars even if the coexistence of hadrons and quarks takes place in the core. However, in the present calculation the transition to pure quark matter does not occur in stable neutron stars. Furthermore, the lower bound of the critical chemical potential of the quark-hadron transition at zero temperature turns out to be around 1.5 GeV in order to be consistent with the recent observed neutron star data.