52 research outputs found
Universality in adsorbate ordering on nanotube surfaces
Numerically efficient transfer matrix technique for studying statistics of
coherent adsorbates on small nanotubes has been developed. In the framework of
a realistic microscopic model fitted to the data of ab initio calculations
taken from literature sources, the ordering of potassium adsorbate on (6,0)
single-walled carbon nanotube has been studied. Special attention has been
payed to the phase transition-like abrupt changes seen in the adsorption
isotherms at low temperature. It has been found that the behavior during the
transitions conforms with the universality hypothesis of the theory of critical
phenomena and is qualitatively the same as in the one dimensional Ising model.
Quantitatively the critical behavior can be fully described by two parameters.
Their qualitative connection with the properties of interphase boundaries is
suggested but further research is needed to develop a quantitative theory.Comment: 11 pages, 6 figures; some typos correcte
Transfer matrix solution of the Wako-Sait\^o-Mu\~noz-Eaton model augmented by arbitrary short range interactions
The Wako-Sait{\^o}-Mu\~noz-Eaton (WSME) model, initially introduced in the
theory of protein folding, has also been used in modeling the RNA folding and
some epitaxial phenomena. The advantage of this model is that it admits exact
solution in the general inhomogeneous case (Bruscolini and Pelizzola, 2002)
which facilitates the study of realistic systems. However, a shortcoming of the
model is that it accounts only for interactions within continuous stretches of
native bonds or atomic chains while neglecting interstretch (interchain)
interactions. But due to the biopolymer (atomic chain) flexibility, the
monomers (atoms) separated by several non-native bonds along the sequence can
become closely spaced. This produces their strong interaction. The inclusion of
non-WSME interactions into the model makes the model more realistic and
improves its performance. In this study we add arbitrary interactions of finite
range and solve the new model by means of the transfer matrix technique. We can
therefore exactly account for the interactions which in proteomics are
classified as medium- and moderately long-range ones.Comment: 15 pages, 2 figure
Accelerated kinetic Monte Carlo algorithm for diffusion limited kinetics
If a stochastic system during some periods of its evolution can be divided
into non-interacting parts, the kinetics of each part can be simulated
independently. We show that this can be used in the development of efficient
Monte Carlo algorithms. As an illustrative example the simulation of
irreversible growth of extended one dimensional islands is considered. The new
approach allowed to simulate the systems characterized by parameters superior
to those used in previous simulations.Comment: 4 pages, 4 figures, to be published in Phys. Rev.
Magnetic reordering in the vicinity of a ferromagnetic/antiferromagnetic interface
The magnetic arrangement in the vicinity of the interface between a
ferromagnet and an antiferromagnet is investigated, in particular its
dependence on the exchange couplings and the temperature. Applying a Heisenberg
model, both sc(001) and fcc(001) lattices are considered and solved by a mean
field approximation. Depending on the parameter values a variety of different
magnetic configurations emerge. Usually the subsystem with the larger ordering
temperature induces a magnetic order into the other one (magnetic proximity
effect). With increasing temperature a reorientation of the magnetic
sublattices is obtained. For coupled sc(001) systems both FM and AFM films are
disturbed from their collinear magnetic order, hence exhibit a similar
behavior. This symmetry is absent for fcc(001) films which, under certain
circumstances, may exhibit two different critical temperatures. Analytical
results are derived for simple bilayer systems.Comment: accepted for publication in Eur. Phys. J.
In-plane magnetic reorientation in coupled ferro- and antiferromagnetic thin films
By studying coupled ferro- (FM) and antiferromagnetic (AFM) thin film
systems, we obtain an in-plane magnetic reorientation as a function of
temperature and FM film thickness. The interlayer exchange coupling causes a
uniaxial anisotropy, which may compete with the intrinsic anisotropy of the FM
film. Depending on the latter the total in-plane anisotropy of the FM film is
either enhanced or reduced. Eventually a change of sign occurs, resulting in an
in-plane magnetic reorientation between a collinear and an orthogonal magnetic
arrangement of the two subsystems. A canted magnetic arrangement may occur,
mediating between these two extremes. By measuring the anisotropy below and
above the N\'eel temperature the interlayer exchange coupling can be
determined. The calculations have been performed with a Heisenberg-like
Hamiltonian by application of a two-spin mean-field theory.Comment: 4 pages, 4 figure
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