Medea Vasp Download
Simulation Methods and Validation | |
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| Session chair: | Descalle, Marie-Anne,(Lawrence Livermore National Laboratory (LLNL), Livermore, USA); Brown, David, A.(Brookhaven National Laboratory, National Nuclear Data Center, Upton, USA) |
| Shortcut: | N-12 |
| Date: | Tuesday, 29 October, 2019, 1:40 PM |
| Room: | Charter 3 |
| Session type: | NSS Session |
Recent simulation R&D and validation tests
MedeA ® VASP 5.2 VASP 5.2, first released in mid 2009, represents a breakthrough in the calculation of electronic and optical properties for semiconductors and insulators of industrial importance. This is based on an efficient implementation of hybrid functionals and the GW methods. The MedeA Interface Builder helps to identify and build twist grain boundaries as well as coherent, and/or semi-coherent interfaces. It produces periodic, commensurate cells, which may be used as direct input for MedeA’s compute work flows, engaging VASP, LAMMPS, or any. I want to know whether there are some free GUI mode DFT software packages like MedeA VASP. Thank you in advance. DFT Calculations. Go to this following website where you can download the. I am trying to create surface of WO3 from VASP MedeA software when I am creating 100, 010, 001 surface with 3 layers then POSCAR is showing 24 Tungsten (W) atoms and 72 Oxygen (O) atoms that is.
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Contents
| 1:40 PM | N-12-01 | Atomic Data in EXFOR(#1101)B. Pritychenko1, D. A. Brown1 1 Brookhaven National Laboratory, National Nuclear Data Center, Upton, New York, United States of America Content The EXchange FORmat (EXFOR) experimental nuclear reaction database provides access to the wealth of low- and intermediate-energy nuclear reaction physics data. This resource is based on numerical data sets and bibliographical information of 22,615 experiments since the beginning of nuclear science. The principles of the computer database organization, its extended contents and recent data developments are described. New plans for the atomic data compilation, storage, and dissemination are presented. Keywords: atomic data, compilations, nuclear reaction data, nuclear databases |
| 1:58 PM | N-12-02 | Photoelectric cross sections: validation tests of recent calculation methods(#1783)M. G. Pia1, T. Basaglia2, M. C. Han3, P. Saracco1 1 INFN - Istituto Nazionale di Fisica Nucleare, Sezione di Genova, Genova, Italy Content Several evolutions have recently occurred, concerning photoionization cross sections, which affect the simulation of the photoelectric effect in Monte Carlo codes: revised atomic binding energies, included in the last version of the Evaluated Atomic Data Library released in ENDF/B, affect the position of absorption edges; a detailed formulation of the theory of the photoeffect has become available in a form that is suitable for precise computations; new parameterizations similar to the empirical Biggs-Lighthill formulation have been released in Geant4. These evolutions motivate additional validation tests, which complement those published in 2016. The new cross section formulations are compared with a large set of experimental data collected from the literature, using rigorous statistical methods. A further stage of categorical data analysis determines the state of the art of photoelectric cross section calculations among the various available options. These results provide guidance to the maintainers and the users of Monte Carlo codes to optimize the accuracy of the simulation of experimental scenarios involving photon interactions. Keywords: Cross section, Photoionization, Monte Carlo Simulation, photons |
| 2:16 PM | N-12-03 | Ionization Density-Dependent Scintillation Pulse Shape and Proportionality for Single Decay-Component LaBr3:Ce: Modelling with Transport and Rate Equations(#2705)J. Cang1, M. Zeng1, Y. Li1, X. Zheng1, Y. Gan1, Y. Liu1 1 Tsinghua University, Beijing, China Content Kingdom and lords mod apk old version. Pulse shape discrimination (PSD) is usually achieved using the different fast and slow decay components of inorganic scintillators, such as BaF2, CsI:Tl, etc. However, LaBr3:Ce is considered to not possess different components but has been proved to have the capability of discriminating gamma and alpha events using fast digitizers at room temperature. The physical mechanism of such PSD capability of LaBr3:Ce was still unclear. A model of excitation transport and interaction in a particle track is established to explain such small pulse shape differences in LaBr3:Ce result from different excitation densities. This model takes into account processes of hot and thermalized carrier diffusion, electric-field transport, energy transfer, nonlinear quenching, and radiative recombination. In particular, besides the nonlinear quenching of self-trapped excitons (STE), the nonlinear quenching of excited rare earth ions, Ce, is confirmed herein for the first time to contribute observable ionization α/γ pulse shape differences. With one parameter set, the model reproduces multiple observables of LaBr3:Ce scintillation response, including the ionization density-dependent pulse shape differences, the proportionality response of electrons and quenching factor of alpha particles. Moreover, the model also provides insight on the competition processes of excitations in the track, which can also explain the corelation between proportionality (energy resolution) response and Ce concentration and forecast the generality of ionization density-dependent pulse shape differences in other fast inorganic scintillators, such as LYSO and CeBr3. Keywords: LaBr3:Ce scintillator, Dynamic Model, Scintillation Mechanism, Pulse Shape Discrimination |
| 2:34 PM | N-12-04 | Modelling Photocathode Performance using Density Functional Theory(#2709)J. O. Williams1, J. S. Lapington1, R. Campion2, C. T. Foxon2 1 University of Leicester, Space Research Centre, Department of Physics and Astronomy, Leicester, United Kingdom Content The structure and composition of a crystalline material can strongly affect electronic properties such as the electron affinity and the work function. By tailoring the properties of the material, it is possible to optimise materials as a photocathode for a wide range of applications, including defence, security and remote sensing. The application of molecular beam epitaxy to photocathode deposition allows much improved control over photocathode composition and structure compared to traditional manufacturing methods. We describe the application of density functional theory (DFT) to model photocathode performance and present results from simulations of photocathode materials. DFT modelling was carried out using MEDEA-VASP DFT simulation software, and included preliminary investigations using DFT on different orthorhombic and cubic crystal structure alloys to develop techniques to model changes in stoichiometry and evaluate change to electron affinity; a crucial parameter for high performance photocathodes. VASP simulations are presented and compared to experimental results obtained using specially constructed test cells. The performance of polycrystalline materials with different stoichiometry and layer geometry are evaluated using DFT with experimentally obtained material parameters, and compared with experimental results. Keywords: photocathode, density functional theory, modelling, quantum efficiency |
| 2:52 PM | N-12-05 | Monte Carlo Modeling of Electron Multiplication in Amorphous Silicon Based Microchannel Plates(#2712)J. Löffler1, J. Thomet1, C. Ballif1, N. Wyrsch1 1 Ecole Polytechnique Fédérale de Lausanne (EPFL), Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Neuchâtel, Neuchâtel, Switzerland Content Amorphous silicon based microchannel plates are being developed to overcome performance limits of conventional microchannel plates. They offer a new flexibility and ease of fabrication. A comprehensive AMCP model is being developed to analyze the behavior of AMCPs. It includes Monte Carlo simulation of secondary electron emission distribution as a function of energy and angles and finite element analysis multiphysics software to compute electron trajectories. The paper presents the results of Monte Carlo simulations of secondary emission functions in silicon and the high secondary emissive material Al2O3 and we discuss the gain and potential performance as a function of geometry of such devices. The validity of the Eberhardt’s model for the analysis of AMCPs is also addressed. Keywords: Radiation Detectors, Microchannel Plate, Secondary Electron Emission, Monte Carlo Methods |
| 3:10 PM | N-12-06 | GEANT4 simulation of electron energy deposition: recent evolutions in validation tests(#1333)M. G. Pia1, T. Basaglia2, M. C. Han3, G. Hoff4, E. Ronchieri5, P. Saracco1 1 INFN - Istituto Nazionale di Fisica Nucleare, Sezione di Genova, Genova, Italy Content Accurate simulation of the energy deposited by electrons in matters is an essential requirement of general-purpose Monte Carlo codes, due to its importance in a wide variety of experimental applications in diverse fields, from fundamental physics to instrumentation R&D, dosimetry and other applied physics areas. A set of experimental measurements, specifically performed at the Sandia Laboratory approximately four decades ago as benchmarks for Monte Carlo simulation of electron energy deposition, still represents the most authoritative reference for the validation of the simulation of this observable. Geant4 capability of reproducing the experimental Sandia data was quantitatively documented for previous Geant4 versions: 8.1 and 9.1 to 9.6. Statistical analysis of the simulated and experimental data distributions highlighted differences in compatibility with experiment across the various physics configurations and Geant4 versions used in the simulation, not always fulfilling the expectation of improvement in the evolution of Geant4 version releases. Preliminary investigations concerning Geant4 versions 10.0 to 10.4 hinted to some improvements in the compatibility between simulation and experiment. This presentation will document a thorough validation test of the simulation of electron energy deposition based on Geant4 versions 10.0 to 10.5 by means of rigorous statistical inference methods. The impact of the results on experimental applications will be discussed. Keywords: Monte Carlo simulation, electron, validation, dosimetry |
Requests for technical support from the VASP group should be posted in the VASP-forum.
- 2Input
- 3Calculation
Task
In this example the nucleophile substitution of a Cl- by another Cl- in CH3Cl is simulated using bluemoon sampling.
Input
POSCAR
In the blue moon sampling method several POSCAR files are used for different values of the collective variable.
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KPOINTS
- For isolated atoms and molecules interactions between periodic images are negligible (in sufficiently large cells) hence no Brillouin zone sampling is necessary.
INCAR
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- The setting LBLUEOUT=.TRUE. tells VASP to write out the information needed for the computation of free energies.
Calculation
In the blue moon method, the free energy difference is computed by integration of the free energy gradients computed for several points differing in the value of the collective variable distributed between known inital and final states. The gradients for each point are computed within a constrained molecular dynamics simulation (note the value of STATUS=0 for the collective variable defined in the ICONST file).
Running the calculation
The mass for hydrogen in this example is set 3.016 a.u. corresponding to the tritium isotope. This way larger timesteps can be chosen for the MD (note that the free energy is independent of the masses of atoms). The simulation for each of the points along the reaction coordinate is performed in a separate directory called 1, 2, .., 7. These are created automatically by the run script. For practical reasons, we split our (presumably long) blue moon calculation into shorter runs of length of 1000 fs (NSW=1000; POTIM=1). This is done automatically in the script run which looks as follows:
Free-energy profile
The free energy gradient is obtained as a ratio of two averages (see Constrained molecular dynamics). This is done by the script fgradBM.sh, which writes the free energy gradient vs. the collective variable to the file grad.dat:
To execute that script type:
For our purposes, a simple trapezoidal rule can be used for the integration of gradients. For accurate calculations, more sohpisticated integration schemes should be considered.The free energy vs. collective variable is obtained by forward integration using the script integrateForward.py:
To execute that script type and write to the file free_energy.dat:
Finally to plot that file type:
The free energy profile should look like the following:
Note that much longer simulations should be performed (typically a few tens or hundreds of ps) in order to achieve well converged averages needed in accurate calculations.