Person: Fernández Pérez, Luis Antonio
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First Name
Luis Antonio
Last Name
Fernández Pérez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física Teórica
Area
Física Teórica
Identifiers
57 results
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Now showing 1 - 10 of 57
Item Tethered Monte Carlo: computing the effective potential without critical slowing down(Nuclear physics B, 2009) Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Yllanes, D.We present Tethered Monte Carlo, a simple, general purpose method of computing the effective potential of the order parameter (Helmholtz free energy). This formalism is based on a new statistical ensemble, closely related to the micromagnetic one, but with an extended configuration space (through Creutz-like demons). Canonical averages for arbitrary values of the external magnetic field are computed without additional simulations. The method is put to work in the two-dimensional Ising model, where the existence of exact results enables us to perform high precision checks. A rather peculiar feature of our implementation, which employs a local Metropolis algorithm, is the total absence, within errors, of critical slowing down for magnetic observables. Indeed, high accuracy results are presented for lattices as large as L = 1024.Item Phase diagram and influence of defects in the double perovskites(Physical review B, 2003) Alonso, J. L.; Fernández Pérez, Luis Antonio; Guinea, F.; Lesmes, F.; Martín Mayor, VíctorThe phase diagram of the double perovskites of the type Sr_(2-x)La_(x)FeMoO_(6) is analyzed, with and without disorder due to antisites. In addition to an homogeneous half metallic ferrimagnetic phase in the absence of doping and disorder, we find antiferromagnetic phases at large dopings, and other ferrimagnetic phases with lower saturation magnetization, in the presence of disorder.Item Ion kinetic transport in TJ-II(AIP conference proceedings: large scale simulations of complex systems, condensed matter and fusion plasma, 2008) Velasco, J. L.; Castejón, F.; Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Tarancón, A.The ion Drift Kinetic Equation (DKE) which describes the ion coUisional transport is solved for the TJ-II device plasmas. This non-linear equation is computed by peribrming a mean field iterative calculation. In each step of the calculation, a Fokker-Planck equation is solved by means of the Langevin approach: one million particles are followed in a realistic TJ-II magnetic configuration, taking into account collisions and electric field. This allows to avoid the assumptions made in the usual neoclassical approach, namely considering radially narrow particle trajectories, diffusive transport, energy conservation and infinite parallel transport. As a consequence, global features of transport, not present in the customary neoclassical models, appear: non-diffusive transport and asymmetries on the magnetic surfaces.Item Correspondence between long-range and short-range spin glasses(Physical review B, 2012) Baños, R.A.; Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Young, A.P.We compare the critical behavior of the short-range Ising spin glass with a spin glass with long-range interactions which fall off as a power σ of the distance. We show that there is a value of σ of the long-range model for which the critical behavior is very similar to that of the short range model in four dimensions. We also study a value of σ for which we find the critical behavior to be compatible with that of the three-dimensional model, although we have much less precision than in the four-dimensional case.Item Comment on "Evidence of Non-Mean-Field-Like Low-Temperature Behavior in the Edwards-Anderson Spin-Glass Model"(Physical review letters, 2013) Billoire, A.; Fernández Pérez, Luis Antonio; Maiorano, A.; Marinari, E.; Martín Mayor, Víctor; Parisi, G.; Ricci-Tersenghi, F.; Ruiz Lorenzo, J.J.; Yllanes, D.Item Critical properties of the four-state commutative random permutation glassy Potts model in three and four dimensions(Physical review B, 2008) Fernández Pérez, Luis Antonio; Maiorano, A.; Marinari, E.; Martín Mayor, Víctor; Navarro, D.; Sciretti, D.; Tarancón, A.; Velasco, J. L.We investigate the critical properties of the four-state commutative random permutation glassy Potts model in three and four dimensions by means of Monte Carlo simulations and a finite-size scaling analysis. By using a field programmable gate array, we have been able to thermalize a large number of samples of systems with large volume. This has allowed us to observe a spin-glass ordered phase in d=4 and to study the critical properties of the transition. In d=3, our results are consistent with the presence of a Kosterlitz-Thouless transition, but also with different scenarios: transient effects due to a value of the lower critical dimension slightly below 3 could be very important.Item Optimized Monte Carlo method for glasses(Philosophical magazine, 2007) Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Verrocchio, P.A new Monte Carlo algorithm is introduced for the simulation of supercooled liquids and glass formers, and tested in two model glasses. The algorithm thermalizes well below the Mode Coupling temperature and outperforms other optimized Monte Carlo methods.Item Numerical test of the Cardy-Jacobsen conjecture in the site-diluted Potts model in three dimensions(Physical review B, 2012) Fernández Pérez, Luis Antonio; Gordillo Guerrero, A.; Martín Mayor, Víctor; Ruiz Lorenzo, J.J.We present a microcanonical Monte Carlo simulation of the site-diluted Potts model in three dimensions with eight internal states, partly carried out on the citizen supercomputer Ibercivis. Upon dilution, the pure model’s first-order transition becomes of the second order at a tricritical point. We compute accurately the critical exponents at the tricritical point. As expected from the Cardy-Jacobsen conjecture, they are compatible with their random field Ising model counterpart. The conclusion is further reinforced by comparison with older data for the Potts model with four states.Item On the universality class of monopole percolation in scalar QED(Physics letters B, 1999) Fernández Pérez, Luis Antonio; Martín Mayor, VíctorWe study the critical properties of the monopole-percolation transition in U(1) lattice gauge theory coupled to scalars at infinite (β = 0) gauge coupling. We find strong scaling corrections in the critical exponents that must be considered by means of an infinite-volume extrapolation. After the extrapolation, our results are as precise as the obtained for the four dimensional site-percolation and, contrary to previously stated, fully compatible with them.Item Equilibrium fluid-solid coexistence of hard spheres(Physical review letters, 2012) Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Seoane Bartolomé, Beatriz; Verrocchio, P.We present a tethered Monte Carlo simulation of the crystallization of hard spheres. Our method boosts the traditional umbrella sampling to the point of making practical the study of constrained Gibbs’ free energies depending on several crystalline order parameters. We obtain high-accuracy estimates of the fluid-crystal coexistence pressure for up to 2916 particles (enough to accommodate fluid-solid interfaces). We are able to extrapolate to infinite volume the coexistence pressure [p_(co) = 11.5727(10)k_(B)T/σ^(3)] and the interfacial free energy [γ_({100}) = 0.636(11)k_(B)T/σ^(2)].