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1

Critical Behaviour of Some 2D Lattice Models

100%

Kamieniarz G., Blöte H., Dekeyser R.

Acta Physica Polonica A

|

1994

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vol. 85

|

issue 2

389-393

EN

The density series of the non-interacting hard-square lattice gas model are reanalyzed by the ratio, Dlog Padé and differential approximant methods. The problem of poor consistency between series and other results is resolved. Transfer matrix calculations are performed, implementing both finite-size scaling and conformal invariance. Very accurate estimates of the critical exponents y_{t}, and y_{h} are obtained in agreement with Ising universality. Furthermore, an improvement of the value of the critical density ρ_{c} is found. In addition, the universal critical-point ratios of the square of the second and the fourth moment of the magnetization for ferromagnetic Ising models on the square and on the triangular lattice with periodic boundary conditions are reported.

2

Effective Field Methods for Magnetic Systems

100%

Kamieniarz G., Dekeyser R., Musiał G.

Acta Physica Polonica A

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1994

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vol. 85

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issue 2

413-417

EN

The self-consistency conditions inherent in the mean-field approximation are extended to take into account some pair correlations. Ii is shown that this extension is systematically improvable and applicable to the spin systems with short-range interactions in the entire temperature region. With two correlations included and the renormalization-group ideas implemented, the critical properties of the Ising model are satisfactorily revealed. Moreover, the improved estimates of the thermodynamical quantities for the quantum linear XY model from the finite-size calculations are found down to very low temperatures.

3

Improved Phase Diagrams of Ashkin-Teller Model

88%

Pawlicki P., Kamieniarz G., Kozlowski P., Dekeyser R., Rogiers J.

Acta Physica Polonica A

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1997

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vol. 92

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issue 2

453-458

EN

The phase diagram of the Askhin-Teller model in two dimensions is determined. Numerical calculations are performed for the simple square L × L lattice using transfer matrix technique. Exploiting finite-size scaling all unknown critical lines were obtained with good accuracy. An extended version of the Ashkin-Teller model is also considered within the molecular field renormalization group method and the critical surface for three-parameter odd-parity Hamiltonian is calculated.

4

Quantum Effects and Critical Behavior in Low-Dimensional Spin-1/2 Systems

88%

Kamieniarz G., Musial G., Dębski L., Bieliński M., Dekeyser R.

Acta Physica Polonica A

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1997

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vol. 92

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issue 2

445-447

EN

The critical coupling and spontaneous magnetization curve for the 2D-Ising model are calculated using the effective-field method with correlations. An application of the method to the quantum S=1/2 1D-Heisenberg model is presented and reliable low-temperature estimates of the specific heat are evaluated.

5

Direct Simulations of the Quantum Model for CsNiF_{3}

88%

Caramico D'Auria A., Esposito F., Esposito U., Kamieniarz G., Dekeyser R.

Acta Physica Polonica A

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1994

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vol. 85

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issue 2

409-412

EN

We address the problem of reliability of a finite-chain technique for CsNiF_{3}. We investigate the effect of the boundary conditions, completely neglected so far, and apply a new extrapolation procedure appropriate for quantities showing non-monotonic behaviour. From a detailed analysis of the specific heat existing theoretical estimates for the model parameters are discriminated and a strong evidence for the reliability of the direct finite-chain technique predictions is presented.

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5 Acta Physica Polonica A

2 1997

3 1994

5 Dekeyser R.

5 Kamieniarz G.

1 Bieliński M.

1 Blöte H.

1 Caramico D'Auria A.

1 Dębski L.

1 Esposito F.

1 Esposito U.

1 Kozlowski P.

1 Musial G.

1 Musiał G.

1 Pawlicki P.

1 Rogiers J.

Critical Behaviour of Some 2D Lattice Models

Effective Field Methods for Magnetic Systems

Improved Phase Diagrams of Ashkin-Teller Model

Quantum Effects and Critical Behavior in Low-Dimensional Spin-1/2 Systems

Direct Simulations of the Quantum Model for CsNiF_{3}