DDD Energy Manual

DDD Energy calculation

DDD Energy Manual

Nicolas Bertin

May 2018

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This page details how to use the DDD energy calculation tool (see Bertin and Cai, JMPS, 2018) to compute the stored energy associated with periodic, discrete dislocation structures generated from ParaDiS.

Compilation

The DDD energy calculation tool is located in directory utilities/energy of the ParaDiS code. The compilation of the code is performed with

 cd utilities/energy
 make

Make sure that the compilation mode is set to SERIAL in the global makefile.setup file before compiling. Use flag -D_ENERGY_GPU to enable GPU computations. Successful compilation will create executable paradiseng in the global bin/ folder.

Usage

Input files

The DDD energy tool requires the same input files as the ParaDiS code, i.e. a control file and a data file. The calculation of the energy is performed using the following command:

 ./paradiseng -d file.data file.ctrl

The control file for the energy tool paradiseng requires some additional parameters compared to the original control files used for ParaDiS simulations. There are 6 additional parameters that are specific to the energy calculation and that must be specified in the control file:

• numPBCimg: number of periodic images (in each direction) to be considered in the calculation
• numGrid: resolution of the grid (in each direction) used to calculate the volume-based energy
• rclarge1: value for the first large core radius used in the regularization procedure
• rclarge2: value for the second large core radius used in the regularization procedure
• GPU: toogle to enable GPU-accelerated calculations
• spectral: toogle to use the spectral approach (see Bertin, arXiv, 2018) to evaluate the volume-based energy (very efficient). When the spectral method is used, the number of periodic images (numPBCimg) is ignored, and the values of the large core radius (rclarge1 and rclarge2) are automatically re-calculated based on the grid resolution numGrid. The spectral method is not compatible with GPU calculation as of now.

As an example, the following lines can be added at the end of any existing control file in order to use it with tool paradiseng:

 ##----------------------------------
 ## ENERGY
 ##----------------------------------
 numPBCimg = 3
 numGrid = 64
 rclarge1 = 1000.0
 rclarge2 = 1500.0
 GPU = 1
 spectral = 0

Examples

Examples of input files to compute the energy of DDD configurations are provided in

 utilities/energy/examples

The examples can be run using the following commands:

 cd utilities/energy/examples
 ../../../bin/paradiseng -d taylor_edge_20.data taylor_edge_20.ctrl 
 ../../../bin/paradiseng -d rs0001.data rs0001.ctrl

The value of the stored energy is outputted in the console and in file energy.dat. File energy.dat is created in the output directory of the simulation (specified with control parameter dirname). The first column is the dislocation density ($m^{-2}$), and the second column is the value of the stored energy ($J/b^{3}$).