Local magnetic structure due to inhomogeneity of interaction in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>S</mml:mi><mml:mo>=</mml:mo><mml:mfrac><mml:mrow><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:mfrac></mml:math>antiferromagnetic chains

Nishino, Masamichi; Onishi, Hiroaki; Roos, Pascal; Yamaguchi, Kizashi; Miyashita, Seiji

doi:10.1103/physrevb.61.4033

Cited by 25 publications

(30 citation statements)

References 30 publications

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“…For example, it has been applied to elucidate quantum effects of one-dimensional infinite magnetic chains consisting of molecular spins [55]: note that Haldane conjecture [56] predicts different magnetic behaviors of integer (S a = n) and half-integer (S a = n + 1/2) magnetic chains. The quantum Monte Carlo [2,57] and density matrix renormalized group methods have been employed for numerical simulations of the chains. Since the possible mechanism of singlet pair formation is essential in low-dimensional quantum spins, magnetic impurity problem is very interesting [58].…”

Section: Discussionmentioning

confidence: 99%

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Yamaguchi

Kawakami

Takano

et al. 2002

Int J of Quantum Chemistry

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125

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Analytical expressions of total energies, effective exchange integrals, polyradical character, spin density, unpaired electron density, and information entropy are derived for allyl radical dimers and trimers on the basis of the Hubbard model in order to elucidate interrelationships among several broken-symmetry and symmetry-adapted approaches to molecular magnetism. Ab initio unrestricted Hartree-Fock and hybrid density functional theory (DFT) calculations of allyl radical dimers to decamers are also carried out for confirmation of characteristics revealed by the analytical investigations. A mesoscopic hydrogen radical cluster with 50 radical sites is studied by the ab initio hybrid DFT methods to elucidate functional behaviors of the above quantities with change of interatomic distance. The potential curves for the lowest and highest spin states of the cluster by these methods are depicted for the purpose. Implications of the present computational results are discussed in relation to size-consistent spin projection and size effects on effective exchange interactions in mesoscopic radical clusters.

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Section: Discussionmentioning

confidence: 99%

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Yamaguchi

Kawakami

Takano

et al. 2002

Int J of Quantum Chemistry

Self Cite

125

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“…If desired, one can artificially restrict the simulation to some sector of phase space, e.g. to the "canonical ensemble" of constant magnetization, by prohibiting updates that leave this sector, or one can select such sectors a posterior [64,65]. (See also section 4.3).…”

Section: Summary Of the Loop Algorithmmentioning

confidence: 99%

“…It is also possible, and can reduce autocorrelations, to allow the number of worldlines to fluctuate, and afterwards treat each subset of configurations with a certain number of worldlines as a canonical simulation [64,65].…”

Section: Asymmetric Hamiltonians: Magnetic Field Chemical Potentialmentioning

confidence: 99%

“…Random systems have become accessible at sufficiently low temperatures and large system sizes, in-cluding the necessary averaging over disorder realizations. Bond disorder in chains [36,65,[172][173][174][175], bond dilution in 2d systems [144,176,177] and coupled layers [145], as well as random nonmagnetic impurities in ladders [178][179][180], coupled ladders [181], and two-dimensional systems [142,143,146,151,[182][183][184] have been investigated. Frustrated models with a sign problem have been simulated by making use of the increased precision [42, 107,160] and by removing the sign problem in a semifrustrated case [32].…”

Section: Some Applicationsmentioning

confidence: 99%

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The loop algorithm

Evertz

2003

Advances in Physics

289

355

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A review of the Loop Algorithm, its generalizations, and its relation to some other Monte Carlo techniques is given. The loop algorithm is a Quantum Monte Carlo procedure which employs nonlocal changes of worldline configurations, determined by local stochastic decisions. It is based on a formulation of quantum models of any dimension in an extended ensemble of worldlines and graphs, and is related to Swendsen-Wang algorithms. It can be represented directly on an operator level, both with a continuous imaginary time path integral and with the stochastic series expansion (SSE). It overcomes many of the difficulties of traditional worldline simulations. Autocorrelations are reduced by orders of magnitude. Grand-canonical ensembles, off-diagonal operators, and variance reduced estimators are accessible. In some cases, infinite systems can be simulated. For a restricted class of models, the fermion sign problem can be overcome. Transverse magnetic fields are handled efficiently, in contrast to strong diagonal ones. The method has been applied successfully to a variety of models for spin and charge degrees of freedom, including Heisenberg and XYZ spin models, hard-core bosons, Hubbard, and t-J-models. Due to the improved efficiency, precise calculations of asymptotic behavior and of quantum critical exponents have been possible.

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“…This simple system is realized in many cases, e.g., the isotropic anti-ferromagnetic Heisenberg chain with odd number of spins which has the doublet in the ground state. 15) Actually V 15 belongs to this category. 13) For this system (2:1), the LZS transition probability of the adiabatic transition is given by,…”

Section: X2 System and Methodsmentioning

confidence: 99%

Magnetic Foehn Effect in Adiabatic Transition

Saito

Miyashita

2001

J. Phys. Soc. Jpn.

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The magnetization process as a response to a sweeping magnetic eld in the thermal environment is investigated by using the quantum master equation. In a slow sweeping velocity region where the system shows quasi-adiabatic motion, a magnetic plateau in the magnetization process has been observed in the recent experiment of V 15 [Phys. Rev. Lett. 84 (2000) 3454]. Although the experiment was explained from a view of small capacity of the phonon heat bath, i.e., the phonon bottleneck eect, we found that a magnetic plateau appears almost regardless of the properties of the heat bath in the quasi-adiabatic transition and the appearance of the plateau is quite universal. We call it 'Magnetic Foehn eect'. On the other hand, the magnetic plateau also appears in a fast sweeping velocity region by the Landau{Zener{Stückelberg mechanism which is dierent from the above mechanism in a slow sweeping region, and we study the crossover between them. We also propose an experiment which claries the structure of coupling to the thermal reservoir.KEYWORDS: nonadiabatic transition, magnetic tunneling x1. IntroductionProperties of quantum dynamics have been studied extensively for nanoscale magnets and also in microscopic system with nanostructure. 1{3) Energy levels as a function of the external eld form many avoided level crossing points. When the eld is swept, the probability of each diabatic state is scattered to other states. Such scattering mechanism is well described by Landau, Zener, and Stükelberg (LZS) mechanism 4{6) where the scattering probability is given as a function of the sweeping velocity and energy gap at the avoided level crossing point. The LZS probability was originally derived for a two-level system. Nevertheless it has been successfully applied to multi-level system to analyze phenomena related to the nonadiabatic transition. 1{3,7{9) However, realistic experiments are always exposed to a thermal environment. Hence the study on the nonadiabatic transition with eects of environment is quite crucial for further understanding of time-dependent phenomena in microscopic systems. For example, in the recent experiments of uniaxial molecular magnets such as Mn 12 and Fe 8 which show a step-wise magnetization process, the dissipative eects cannot be neglected even at very low temperatures.1,2,10) In multilevel systems, the nonadiabatic transitions successively occur at the avoided level crossing points. It was found that in these experiments, the shape of magnetization curve cannot be explained only by the modication of the LZS transition probability. We studied this discrepancy by a quantum master equation and found that even at very low temperatures, the relaxation between levels with the same sign of magnetization easily occurs although it is not allowed in the pure quantum system. 11) As a result of a composite mechanism of nonadiabatic changes of state and a fast relaxation to the ground state, the magnetization process in such molecule magnets shows a step-wise curve which is dierent from the pure quantum cas...

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Local magnetic structure due to inhomogeneity of interaction inS=12antiferromagnetic chains

Cited by 25 publications

References 30 publications

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

The loop algorithm

Magnetic Foehn Effect in Adiabatic Transition

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Local magnetic structure due to inhomogeneity of interaction inS=12antiferromagnetic chains

Cited by 25 publications

References 30 publications

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

The loop algorithm

Magnetic Foehn Effect in Adiabatic Transition

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Product

Resources

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Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)