Eur. Phys. J. B 5, 825-833 (1998)
https://doi.org/10.1007/s100510050508

Competing bulk and surface fields in d = 2 Ising films near bulk criticality: effects of fluctuations^*

¹ Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, Wrocław 2, Poland
² Institute of Physical Chemistry, Polish Academy of Sciences, Department III, Kasprzaka 44/52, 01-224 Warsaw, Poland

Corresponding author: ^a drzewin@apollo.int.pan.wroc.pl

Received: 11 February 1998
Revised: 16 February 1998
Accepted: 17 March 1998
Published online: 15 October 1998

Abstract

The two-dimensional Ising films with bulk H and surface H₁ fields of opposite sign are studied above and close to bulk criticality by the density matrix renormalization group method. This technique, applied recently to d=2 Ising films, allows for very accurate results for the adsorption Γ as a function of the reduced deviation from the critical temperature τ. For strong H₁ three distinct classes of shapes of , determined by the value of the parameter , where L is the width of the film, are found in agreement with earlier predictions [A. Maciołek, A. Ciach, R. Evans, J. Chem. Phys. 108, 9765 (1998)]. For strong and for weak bulk fields is a monotonic function, increasing for strong H and decreasing for weak H, in agreement with scaling analysis and earlier mean-field results. For H between these extreme cases assumes a maximum for and for a depletion occurs, as in recent experiments for critical adsorption in porous materials. For a limited range of H a qualitatively new behavior of is found. In addition to a maximum, a minimum of for appears, which in the mean-field analysis was absent.