13,844 research outputs found
Determining efficient temperature sets for the simulated tempering method
In statistical physics, the efficiency of tempering approaches strongly
depends on ingredients such as the number of replicas , reliable
determination of weight factors and the set of used temperatures, . For the simulated tempering (SP) in
particular -- useful due to its generality and conceptual simplicity -- the
latter aspect (closely related to the actual ) may be a key issue in
problems displaying metastability and trapping in certain regions of the phase
space. To determine 's leading to accurate thermodynamics
estimates and still trying to minimize the simulation computational time, here
it is considered a fixed exchange frequency scheme for the ST. From the
temperature of interest , successive 's are chosen so that the exchange
frequency between any adjacent pair and has a same value .
By varying the 's and analyzing the 's through relatively
inexpensive tests (e.g., time decay toward the steady regime), an optimal
situation in which the simulations visit much faster and more uniformly the
relevant portions of the phase space is determined. As illustrations, the
proposal is applied to three lattice models, BEG, Bell-Lavis, and Potts, in the
hard case of extreme first-order phase transitions, always giving very good
results, even for . Also, comparisons with other protocols (constant
entropy and arithmetic progression) to choose the set are
undertaken. The fixed exchange frequency method is found to be consistently
superior, specially for small 's. Finally, distinct instances where the
prescription could be helpful (in second-order transitions and for the parallel
tempering approach) are briefly discussed.Comment: 10 pages, 14 figure
Influence of disordered porous media in the anomalous properties of a simple water model
The thermodynamic, dynamic and structural behavior of a water-like system
confined in a matrix is analyzed for increasing confining geometries. The
liquid is modeled by a two dimensional associating lattice gas model that
exhibits density and diffusion anomalies, in similarity to the anomalies
present in liquid water. The matrix is a triangular lattice in which fixed
obstacles impose restrictions to the occupation of the particles. We show that
obstacules shortens all lines, including the phase coexistence, the critical
and the anomalous lines. The inclusion of a very dense matrix not only suppress
the anomalies but also the liquid-liquid critical point
- …