41 research outputs found
Correlation Functions of Multisite Interaction Spin-S models on the Bethe-like Lattices
Multisite interaction spin-S models in an external magnetic field are studied
recursively on the Bethe-like lattices. The transfer-matrix method is extended
to calculate exactly the two-spin correlation functions. The exact expressions
for the correlation length and magnetic susceptibility are derived for spin-1/2
models. The singularity of the correlation length with critical index
and the proportionality of magnetic susceptibility to correlation length in the
second order phase transition region of spin-1/2 ferromagnetic models on the
Bethe-like lattices are established analytically.Comment: 13 pages, In Press Int. J. Mod. Phys.
Yang-Lee and Fisher Zeros of Multisite Interaction Ising Models on the Cayley-type Lattices
A general analytical formula for recurrence relations of multisite
interaction Ising models in an external magnetic field on the Cayley-type
lattices is derived. Using the theory of complex analytical dynamics on the
Riemann sphere, a numerical algorithm to obtain Yang-Lee and Fisher zeros of
the models is developed. It is shown that the sets of Yang-Lee and Fisher zeros
are almost always fractals, that could be associated with Mandelbrot-like sets
on the complex magnetic field and temperature planes respectively.Comment: 9 pages, 3 figures; with minor correction
An exact solution on the ferromagnetic Face-Cubic spin model on a Bethe lattice
The lattice spin model with --component discrete spin variables restricted
to have orientations orthogonal to the faces of -dimensional hypercube is
considered on the Bethe lattice, the recursive graph which contains no cycles.
The partition function of the model with dipole--dipole and
quadrupole--quadrupole interaction for arbitrary planar graph is presented in
terms of double graph expansions. The latter is calculated exactly in case of
trees. The system of two recurrent relations which allows to calculate all
thermodynamic characteristics of the model is obtained. The correspondence
between thermodynamic phases and different types of fixed points of the RR is
established. Using the technique of simple iterations the plots of the zero
field magnetization and quadrupolar moment are obtained. Analyzing the regions
of stability of different types of fixed points of the system of recurrent
relations the phase diagrams of the model are plotted. For the phase
diagram of the model is found to have three tricritical points, whereas for there are one triple and one tricritical points.Comment: 20 pages, 7 figure
Universal geometrical factor of protein conformations as a consequence of energy minimization
The biological activity and functional specificity of proteins depend on
their native three-dimensional structures determined by inter- and
intra-molecular interactions. In this paper, we investigate the geometrical
factor of protein conformation as a consequence of energy minimization in
protein folding. Folding simulations of 10 polypeptides with chain length
ranging from 183 to 548 residues manifest that the dimensionless ratio
(V/(A)) of the van der Waals volume V to the surface area A and average
atomic radius of the folded structures, calculated with atomic radii
setting used in SMMP [Eisenmenger F., et. al., Comput. Phys. Commun., 138
(2001) 192], approach 0.49 quickly during the course of energy minimization. A
large scale analysis of protein structures show that the ratio for real and
well-designed proteins is universal and equal to 0.491\pm0.005. The fractional
composition of hydrophobic and hydrophilic residues does not affect the ratio
substantially. The ratio also holds for intrinsically disordered proteins,
while it ceases to be universal for polypeptides with bad folding properties.Comment: 6 pages, 1 table, 4 figure
Yang-Lee Zeros of the Q-state Potts Model on Recursive Lattices
The Yang-Lee zeros of the Q-state Potts model on recursive lattices are
studied for non-integer values of Q. Considering 1D lattice as a Bethe lattice
with coordination number equal to two, the location of Yang-Lee zeros of 1D
ferromagnetic and antiferromagnetic Potts models is completely analyzed in
terms of neutral periodical points. Three different regimes for Yang-Lee zeros
are found for Q>1 and 0<Q<1. An exact analytical formula for the equation of
phase transition points is derived for the 1D case. It is shown that Yang-Lee
zeros of the Q-state Potts model on a Bethe lattice are located on arcs of
circles with the radius depending on Q and temperature for Q>1. Complex
magnetic field metastability regions are studied for the Q>1 and 0<Q<1 cases.
The Yang-Lee edge singularity exponents are calculated for both 1D and Bethe
lattice Potts models. The dynamics of metastability regions for different
values of Q is studied numerically.Comment: 15 pages, 6 figures, with correction
Classical phase transitions in a one-dimensional short-range spin model
Ising's solution of a classical spin model famously demonstrated the absence
of a positive-temperature phase transition in one-dimensional equilibrium
systems with short-range interactions. No-go arguments established that the
energy cost to insert domain walls in such systems is outweighed by entropy
excess so that symmetry cannot be spontaneously broken. An archetypal way
around the no-go theorems is to augment interaction energy by increasing the
range of interaction. Here we introduce new ways around the no-go theorems by
investigating entropy depletion instead. We implement this for the Potts model
with invisible states.Because spins in such a state do not interact with their
surroundings, they contribute to the entropy but not the interaction energy of
the system. Reducing the number of invisible states to a negative value
decreases the entropy by an amount sufficient to induce a positive-temperature
classical phase transition. This approach is complementary to the long-range
interaction mechanism. Alternatively, subjecting positive numbers of invisible
states to imaginary or complex fields can trigger such a phase transition. We
also discuss potential physical realisability of such systems.Comment: 29 pages, 11 figure