The Landau Distribution for Charged Particles Traversing Thin Films

The Landau distribution as well as its first and second momenta are well suited for describing the energy loss of charged particles traversing a thin layer of matter. At present, just rational approximations and asymptotic expressions for these functions were obtained. In this paper we present a direct calculation of the integral representation of these functions obtaining perturbative and nonperturvative solutions expressed in terms of fast convergent series. We also provide a simple numerical algorithm which allows to control speed and precision of the results. The testing runs have provided, in reasonable computing times, correct results up to 13-14 significant digits on the density and distribution functions and 9-10 on the first and second momenta. If necessary, this accuracy could be improved by adding more coefficients to the algorithm.Comment: 29 pages, 4 Table

Quark-Antiquark Potential and Generalized Borel Transform

The heavy quark potential and particularly the one proposed by Richardson to incorporate both asymptotic freedom and linear confinement is analyzed in terms of a generalized Borel Transform recently proposed. We were able to obtain, in the range of physical interest, an approximate analytical expression for the potential in coordinate space valid even for intermediate distances. The deviation between our approximate potential and the numerical evaluation of the Richardson's one is much smaller than $\Lambda$ of QCD. The $c\overline{c}$ and $b\overline{b}$ quarkonia energy levels agree reasonably well with experimental data for $c$ and $b$ masses in good agreement with the values obtained from experiments.Comment: 9 pages, 3 Tabl

Generalized Borel Transform Technique in Quantum Mechanics

We present the Generalized Borel Transform (GBT). This new approach allows one to obtain approximate solutions of Laplace/Mellin transform valid in both, perturbative and non perturbative regimes. We compare the results provided by the GBT for a solvable model of quantum mechanics with those provided by standard techniques, as the conventional Borel sum, or its modified versions. We found that our approach is very efficient for obtaining both the low and the high energy behavior of the model.Comment: 13 pages, 2 figure

Generalized Borel transform technique in quantum mechanics

We present the Generalized Borel Transform (GBT). This new approach allows one to obtain approximate solutions of Laplace/Mellin transform valid in both, perturbative and non-perturbative regimes. We compare the results provided by the GBT for a solvable model of quantum mechanics with those provided by standard techniques, as the conventional Borel sum, or its modified versions. We found that our approach is very efficient for obtaining both the low and the high energy behavior of the model.Facultad de Ciencias Exacta

Fast calculation of thermodynamic and structural parameters of solutions using the 3DRISM model and the multi-grid method

In the paper a new method to solve the tree-dimensional reference interaction site model (3DRISM) integral equations is proposed. The algorithm uses the multi-grid technique which allows to decrease the computational expanses. 3DRISM calculations for aqueous solutions of four compounds (argon, water, methane, methanol) on the different grids are performed in order to determine a dependence of the computational error on the parameters of the grid. It is shown that calculations on the grid with the step 0.05\Angstr and buffer 8\Angstr give the error of solvation free energy calculations less than 0.3 kcal/mol which is comparable to the accuracy of the experimental measurements. The performance of the algorithm is tested. It is shown that the proposed algorithm is in average more than 12 times faster than the standard Picard direct iteration method.Comment: the information in this preprint is not up to date. Since the first publication of the preprint (9 Nov 2011) the algorithm was modified which allowed to achieve better results. For the new algorithm see the JCTC paper: DOI: 10.1021/ct200815v, http://pubs.acs.org/doi/abs/10.1021/ct200815

A java application to characterize biomolecules and nanomaterials in electrolyte aqueous solutions

The electrostatic, entropic and surface interactions between a macroion (nanoparticle or biomolecule), surrounding ions and water molecules play a fundamental role in the behavior and function of colloidal systems. However, the molecular mechanisms governing these phenomena are still poorly understood. One of the major limitations in procuring this understanding is the lack of appropriate computational tools. Additionally, only experts in the field with an extensive background in programming, who are trained in statistical mechanics, and have access to supercomputers are able to study these systems. To overcome these limitations, in this article, we present a free, multi-platform, portable Java software, which provides experts and non-experts in the field an easy and efficient way to obtain an accurate molecular characterization of electrical and structural properties of aqueous electrolyte mixture solutions around both cylindrical- and spherical-like rigid macroions under multiple conditions. These properties include the normalized ions and water density profile distributions, the mean electrostatic potential, the integrated charge, the zeta potential, the electrostatic potential energy, the particle crowding entropy energy, the ion–ion electrostatic direct correlation energy, and the ionic potential of mean force. The Java software does not require outstanding skills and comes with detailed user-guide documentation. The application is based on the so-called Classical Density Functional Theory Solver (CSDFTS), which was successfully applied to a variety of rod-like biopolymers, rigid-like globular proteins, nanoparticles, and nano-rods. CSDFTS implements several electrolyte and macroion models, uses different levels of approximation and takes advantage of high performance Fortran90 routines and optimized libraries. These features enable the software to run on single processor computers at low-to-moderate computational cost depending on the computer performance, the grid resolution, and the characterization of the macroion and the electrolyte solution, among other factors. As a unique feature, the software comes with a graphical user interface (GUI) that allows users to take advantage of the visually guided setup of the required input data to properly characterize the system and configure the solver. Several examples on nanomaterials and biomolecules are provided to illustrate the use of the GUI and the solver performance