Table of contents

Prolegomena

Computer simulations play a major role in science nowadays. Together with Theory and Experiments it allows a better comprehension of natural phenomena by giving information otherwise unreachable. Indeed, computer simulations are applied in almost every branch of science, from physics, chemistry and biology to the study of complex multidisciplinary problems, such as in material science. Today's Brazilian community has many researchers who use computer simulations in the development of their projects. In this context, the Brazilian Meeting on Simulational Physics (BMSP) has been held since 1997, gathering researchers from Brazil and abroad, working in the most diverse branches of physics. The first version of the BMSP took place in Belo Horizonte in 1997, two years later the second BMSP was also held in Belo Horizonte. The third, fourth and fifth editions of the event were held in Ouro Preto in 2003, 2005 and 2007. In 2011, the sixth edition of the BMSP took place in Cuiabá, followed by the seventh in João Pessoa in 2013 and the eighth in Florianópolis in 2015. The ninth edition celebrated the 20th anniversary of the event in 2017 at the ICTP in Natal. This tenth edition event returned to Minas Gerais. The opening was in Belo Horizonte and the remaining days of the meeting occurred in Ouro Preto. Its growth in importance, not only for the Brazilian but also for the international communities, made the present event a Satellite Meeting of the 27th International Conference on Statistical Physics, StatPhys 27, in Buenos Aires, Argentina.

Beside the opportunity for the community working in this area in Brazil to directly interact with scientists of similar interests, we are particularly proud and happy with this XBMSP due to the massive attendance of graduated and undergraduate students.

The topics covered in this meeting were quite varied, addressing the latest simulation techniques used by the most prominent groups in the world. Some covered topics were: Monte Carlo – Molecular Dynamics and Spin Dynamics – Structural and Magnetic Phase transitions – Surface – Nanostructures – Strongly Correlated Systems - Quantum Monte Carlo – Interfaces – Granular Flow - Membranes and Protein Folding – Genomics – Quantum Computing – Free Energy Determination - Biophysics, among others

The conference photograph and logo are available in this pdf.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Microrheology is a technique that have been largely used to investigate viscoelasticity in biological systems. For example, it revealed that filament networks, which are the main component of the citoskeleton of eukaryote cells, show an interesting semisolid viscoelastic response that is characterized by a hardening behaviour at high frequencies. Here, we adopt a computational approach based on microrheology to study the relationship between the Brownian motion of probe particles immersed in a filament network and its viscoelastic response. In particular, we consider a simple model for the filament networks and perform Brownian dynamics simulations to obtain the mean-squared displacement of probe particles, which is used to evaluate the shear moduli G' and G" of the networks. Our numerical results indicate that the proposed numerical approach can reproduce several features observed in experiments, including the sol-gel transition observed when varying the density of filaments, and the aforementioned hardening behaviour at high frequencies.

We use the Auxiliary Field Quantum Monte Carlo technique to perform a simple study of the two dimensional attractive Hubbard model and calculate the total ground state energy to compare with another technique in the literature for U = –4t. Our finite size extrapolated result corroborate the approximated lattice density-functional theory method for this value of U at half-filling. To stabilize the Auxiliary Field Quantum Monte Carlo algorithm one must resort to one of the two decomposition methods: the modified Grand-Schmidt decomposition and the singular value decomposition. Two characteristics like accuracy and total execution time were considered to compare the decomposition algorithms, and the results are presented bellow.

In this work we use a Computational Monte Carlo experiment for modeling the far from equilibrium growth of nanowires from a mixing of two particles species MBE experiment. We observed three distinct phases. There is a low temperature region where nanowires are formed. An intermediate phase, at a higher temperature where the solute floats over the solvent. Above a critical temperature a phase, similar to a paramagnetic phase in magnetic materials shows up. In this region solvent and solute are completely mixed up.

A great triumph of statistical physics in the latter part of the 20th century was the understanding of critical behavior and universality at second-order phase transitions. In contrast, first-order transitions were believed to have no common features. However, we argue that the classic, first-order "spin-flop" transition (between the antiferromagnetic and the rotationally degenerate, canted state) in an anisotropic antiferromagnet in a magnetic field exhibits a new kind of universality. We present a finite-size scaling theory for a first-order phase transition where a continuous symmetry is broken using an approximation of Gaussian probability distributions with a phenomenological degeneracy factor "q" included, where "q" characterizes the relative degeneracy of the ordered phases. Predictions are compared with high resolution Monte Carlo simulations of the three-dimensional, XXZ Heisenberg antiferromagnet in a field to study the finite-size behavior for L×L×L simple cubic lattices. The field dependence of all moments of the order parameters exhibit universal intersections at the spin-flop transition. Our Monte Carlo data agree with theoretical predictions for asymptotic large L behavior. Our theory yields q = π, and we present numerical evidence that is compatible with this prediction. The agreement between the theory and simulation implies a heretofore unknown universality.

Using the fixed-node diffusion quantum Monte Carlo method (FN-DMC), the density functional theory (DFT), and the Hartree-Fock (HF) approximation, we investigate the valence electron binding energies of atomic clusters. Calculations are applied to the metal-doped anionic aluminum clusters ${{\rm{XAl}}}_{4}^{-}$ (X = K, Rb, Ag, and Au) and their vertical detachment energies (VDE) are obtained. A comparison between the FN-DMC results and the HF ones allows us to quantify the electron correlation effects and their impact on the stability of the clusters. The analysis reveals that the electron correlation enhances the vertical detachment energies of the atomic clusters significantly.

A spin-1/2 Ising model, with nearest-neighbor exchange and next-nearest-neighbor superexchange interactions, is proposed to describe the phase diagram of disordered Fe_p-Al_q (p + q = 1) alloys in the body centered cubic lattice. The size of the aluminum clusters have been taken into account in order to induce a superexchange interaction among the Fe atoms. Extensive Monte Carlo simulations have been employed by using a hybrid algorithm consisting of Metropolis spin flip and Wolff cluster algorithm, together with single histograms techniques. A good fit to the experimental phase diagram has been achieved, including the anomalous region for Al concentration in the range q ≤ 0.2.

In this communication we explore the possible effects of statistical fluctuations on the use of the Energy Probability Distribution (EPD) zeros to study phase transitions. In the EPD zeros technique one has to find the roots of a polynomial whose coefficients are given by the EPD - a histogram of energy values obtained in a Monte Carlo simulation, for example. Phase transitions are signalized by the presence of a zero that approaches the point (1,0) in the complex plane. Once the EPD estimations are usually subject to statistical fluctuations and polynomial roots are known to be sensitive to modifications in its coefficients, we have compared the roots of a given polynomial with the roots of a perturbed one, searching for possible impacts on the method. Our results show that although the overall map of zeros is modified, the location of the dominant zero, the one that indicates the presence of a phase transition, is not affected. Indeed, even for 30% perturbation only small modifications in the dominant zero location is observed.

The versatility of carbon-carbon bonds is in charge of various carbon-based structures including numerous possibilities for building fullerenes. Theoretically, it is possible to make any closed surface consisting of C atoms in a number of ways. However, the generation of possible arrangements and, furthermore, calculating the corresponding energetics is a great challenge even for a small molecule. In this context, we develop a genetic-algorithm-based code that can search for exotically shaped fullerenes. Furthermore, we discuss the construction and optimization of the algorithm assisted by some test results.

The continuous ferromagnetic-paramagnetic phase transition in the two-dimensional Ising model has already been excessively studied by conventional canonical statistical analysis in the past. We use the recently developed generalized microcanonical inflection-point analysis method to investigate the least-sensitive inflection points of the microcanonical entropy and its derivatives to identify transition signals. Surprisingly, this method reveals that there are potentially two additional transitions for the Ising system besides the critical transition.

In this work we use the zeros of the energy probability distribution to obtain the critical diagram of the three dimensional (L³) ±J Ising model. Starting with a complete ferromagnetic system we introduce a number of p × L³ antiferromagnetic bonds in the system. The phase diagram, temperature against antiferromagnetic bond concentration (p), is estimated for several values of p. The goal of this preliminary study is to show how it is possible to determine the phase diagram of such a complex model without the need to define any order parameter.

Microcanonical thermostatistics analysis has been introduced as an important method in the study of phase transitions observed in intrinsically small systems, such as folding transitions in proteins and surface adsorption transitions of polymeric chains. Here we consider a lattice model and apply microcanonical analysis to investigate the aggregation transition of a system with anisotropically interacting molecules. By performing multicanonical Monte Carlo simulations we are able to obtain free-energy profiles from where we extract physical quantities related to the aggregation transition such as its transition temperature, latent heat, and free-energy barriers. Our results confirms that the aggregation transition is a first-order type of transition and that it is related to the nucleation of molecules into elongated aggregates. Also, our analysis revealed an unexpected non-monotonic behavior for the free-energy barrier as a function of the anisotropic ratio ξ between strong and weak interactions of the molecules, indicating that the nucleation kinetics might be also influenced by ξ.

A recent theoretical work by Bousquet and collaborators have predicted that ferroelectric ordering could be induced in the rocksalt oxides of alkaline earth metals (BaO, MgO, CaO and SrO) by strain. The expected functional properties present in these strained binary oxides, like polarization, dielectric constant and piezoelectric response, would be comparable to those of typical ferroelectric perovskites. Consequently, the strained binary oxides would be promising materials for fabrication of devices like ferroelectric memories and sensors. One possible way to explore the potential underlying these theoretical predictions is to grow thin and ultra-thin films of these binary oxides under epitaxial strain by choosing an adequate substrate. In such systems the interplay between epitaxial strain and the lack of translational symmetry (limited film thickness) may lead to the formation of interesting (anti)ferroelectric phases. Our goal in this work is to explore the potential structural and functional phase diagram of BaO ultra-thin films (thickness of only 8 BaO layers, ≈ 20 nm) obtained for different values of compressive epitaxial strain and temperature by performing a molecular dynamics investigation. A polarized phase (antipolar) is observed at a compressive strain of -9.0%, wich resists till a melting temperature around 1500 K, which is indeed high for such an ultra-thin film.

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