BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:Computational approaches for electronic properties of semiconducti ng materials and nanostructures DTSTART;VALUE=DATE-TIME:20121018T101500Z DTEND;VALUE=DATE-TIME:20121018T104500Z DTSTAMP;VALUE=DATE-TIME:20261010T220224Z UID:indico-contribution-99-167@indico.ipb.ac.rs DESCRIPTION:Speakers: Nenad Vukmirovic (Scientific Computing Laboratory\, Institute of Physics Belgrade\, University of Belgrade)\nDensity functiona l theory (DFT) provides a reliable theoretical framework for studying the electronic properties of atoms\, molecules\, bulk materials\, surfaces\, i nterfaces\, etc. However\, due to its computational effort\, the calculati ons based on DFT are typically performed only for relatively small molecul es or for crystalline materials where periodicity of the structure can be exploited. There is a wealth of highly relevant systems which are currentl y beyond the reach of standard DFT calculations\, such as\, for example\, disordered conjugated polymers\, inorganic nanocrystals\, and polycrystall ine materials. To study these systems\, one typically needs to do the calc ulation for a supercell containing thousands of atoms to get reliable info rmation about the properties of the system.\n\nThe methods that can be use d to study even such systems will be presented and computational aspects o f the applications of these methods will be discussed. \n\nCharge patching method (CPM) [1] is the method for the construction of electronic charge density of the system that avoids demanding self-consistent DFT calculatio ns. It is based on the idea that electronic charge density in the neighbor hood of an atom depends mainly on its local environment. Such an assumptio n is typically valid in semiconducting and insulating materials without an y long-range charge transfer. The contribution of each atom to electronic charge density of the system is therefore extracted from the calculation o f some small prototype system where atoms have the same environment as in the large system under study. Electronic charge density of the large syste m is then simply obtained by adding the contributions of each atom. With e lectronic charge density at hand\, one gets the single-particle Hamiltonia n by solving the Poisson equation for the Hartree potential and using the local density approximation formula for the exchange-correlation potential .\n\nTo study the electrical properties of the material\, one does not nee d to calculate all the electronic states of the Hamiltonian but only these in the region near the band gap. Overlapping fragments method (OFM) [2] w as developed to efficiently find these states. The method is in particular suited to study disordered conjugated polymers [3]. It is based on the di vison of the system into fragments and the representation of the Hamiltoni an in the basis of molecular orbitals of these fragments. It is typically sufficient to use only a few molecular orbitals of each fragment. This app roach strongly reduces the size of the Hamiltonian matrix that needs to b e diagonalized down to the size of several hundreds.\n\nFinally\, several applications of these methods in the studies of organic solar cell materia ls will be briefly presented.\n\n[1] N. Vukmirovic and L.-W. Wang\, J. Che m. Phys. 128\, 121102 (2008).\n[2] N. Vukmirovic and L.-W. Wang\, J. Chem. Phys. 134\, 094119 (2011).\n[3] N. Vukmirovic and L.-W. Wang\, J. Phys. C hem. B 115\, 1792 (2011).\n\nhttps://events.saifa.rs/event/291/contributio ns/167/ LOCATION:National Library of Serbia URL:https://events.saifa.rs/event/291/contributions/167/ END:VEVENT BEGIN:VEVENT SUMMARY:Reflections on Paralelization of Gravity Inversion DTSTART;VALUE=DATE-TIME:20121018T104500Z DTEND;VALUE=DATE-TIME:20121018T111500Z DTSTAMP;VALUE=DATE-TIME:20261010T220224Z UID:indico-contribution-99-175@indico.ipb.ac.rs DESCRIPTION:Speakers: Neki Frasheri (Polytechnic University of Tirana\, Fa culty of Information Technology)\nIn the paper there is presented a summar y of results obtained for the parallelization of 3D gravity inversion usin g the principle of algorithm CLEAN [Hogborn 1974]\, undertaken in framewor k o f FP7 project HP-SEE. The problem is “ill posed” with the definiti on of [Hadamard 1902].\nThe core of our algorithm consists in cross-calcul ation of the effect of 3D array of underground nodes to each of 2D array g round surface points. The process is iterative\, updating at each iteratio n the mass density of one node with a predefined step in order to decrease of the least squares error. The volume of calculations for each iteration was calculated of the order O (N^5). The number of iterations to obtain t he same anomalous body resulted of the order O (N^3)\, leading to an order of calculations O (N^8). \nExperiments were carried out in two HPC system s – the HPCG system of IICT-BAS in Sofia\, Bulgaria\, and in the SGE sys tem of NIIFI at University of Pécs\, Hungary\, using both OpenMP and MPI. Obtained results confirmed the order of calculations of O (N^8). The abso lute user-time and wall-time was obtained. For moderate sized models with geosection 4000m*4000m*2000m using 3D arrays of 101*101*51 nodes\, using u p to 1\,000 parallel cores\, the run-time reached the level of 100\,000 se conds (27 hours). \nTests with models and field data resulted with clear m ass density contrasts between the anomalous bodies and the medium where th ey were situated\, in the same way as in real geological structures. Tests with multi-bodies geosections indicated the tendency of the algorithm to converge towards single body solutions. \nMPI tests carried out in HPCG sy stem of IICT-BAS showed a systematic time overhead when the number of para llel processes increased from 8 to 32. Hypothesizing that this was caused because of inter-process communication between computer nodes\, a predicti on of potential run-time in multi-cluster MPI grid platforms was undertake n\, taking into consideration the relative low bandwidth of campus and met ropolitan links (compared with the bandwidth of the BUS connecting cores o f a computer node). The extrapolation of data led to the hypothesis that t he increase in cores using multi-cluster grids may not result in reduction of the run-time.\n\nhttps://events.saifa.rs/event/291/contributions/175/ LOCATION:National Library of Serbia URL:https://events.saifa.rs/event/291/contributions/175/ END:VEVENT BEGIN:VEVENT SUMMARY:Using Structured Adaptive Computational Grid for Solving Multidime nsional Computational Physics Tasks DTSTART;VALUE=DATE-TIME:20121018T094500Z DTEND;VALUE=DATE-TIME:20121018T101500Z DTSTAMP;VALUE=DATE-TIME:20261010T220224Z UID:indico-contribution-99-188@indico.ipb.ac.rs DESCRIPTION:Speakers: Peter Bogatencov (RENAM Association)\nIn the work de scribed the algorithm and program for solving multidimensional problems re presented by differential equations with partial derivatives adopted for u sing SEE regional HPC resources. The algorithm based on the AMR method - a daptive mesh refinement of the computational grid. Utilization of AMR meth od can significantly improve the resolution of the difference grid in area s of high interest and accelerate the processes of the multi-dimensional p roblems calculating.\nOne of the methods that allow developing optimized a pplications and speeding up the process of complicated models execution is the method based on adaptive refinement of computational mesh – AMR (Ad aptive Mesh Refinement) method. Many complex problems of continuum mechani cs are numerically solved on structured or unstructured grids. To improve the accuracy of the calculations is necessary to choose a sufficiently sma ll grid (with a small cell size). This leads to the drawback of a substant ial increase of computation time. Therefore\, for the calculations of comp lex problems it is reasonable to use AMR method. That is\, the grid refine ment is performed only in the areas of interest of the structure\, where e .g. the shock waves are generated\, or a complex geometry or other such fe atures exist. Applying AMR the computing time is greatly reducing and the execution of the application on the resulting sequence of nested\, decreas ing nets can be parallelized. We are considering solution of two- and thre e- dimensional tasks of gas dynamics that have obvious practical interest. These solutions can be applied to many nowadays problems. However\, the m aking of three-dimensional calculations for high definition grids requires large computational resources.\nIn all cases\, at the beginning of solvin g the problem we define a way to highlight areas in which we need to const ruct the grid\, and then the program builds a sequence of grids and makes a decision on them. During calculations in the computational area there ar e domains with large gradients of the parameters - such as temperature\, p ressure\, density and others. These areas are contiguous with areas with a smooth behavior of the investigated functions. Therefore\, to reduce the requirements for computing resources a detailed grid with small mesh sizes can be created only in areas of high gradients. Approach to creation of s uch area - adaptive mesh refinement will significantly clarify the definit ion of the multi-dimensional flows features. The proposed AMR method is th e most suitable method of grid generation for solving three-dimensional pr oblem of the collapsing star. \nCalculations using of AMR method based on the hierarchical grid cells\, which can significantly improve the quality of the calculations in the various fields of science and engineering. Prog ram based on AMR technology uses object-oriented approach\, which is avail able in the current version of Fortran 90.\n\nhttps://events.saifa.rs/even t/291/contributions/188/ LOCATION:National Library of Serbia URL:https://events.saifa.rs/event/291/contributions/188/ END:VEVENT END:VCALENDAR