# Elastic: A tool for calculating second-order elastic constants from first principles and for any crystal structure.

Calculations of Solid Properties Using Wien2k Package :: DIFFERENT PROPERTIES :: MECHANICAL AND ELASTIC PROPERTIES

## Elastic: A tool for calculating second-order elastic constants from first principles and for any crystal structure.

Elastic: A tool for calculating second-order elastic constants from first principles and for any crystal structure.

To download the package clik on the link below :

http://exciting.wdfiles.com/local--files/elastic/ElaStic_1.0.tar.gz

## Re: Elastic: A tool for calculating second-order elastic constants from first principles and for any crystal structure.

**ReadMe file :**

**ABOUT**

**=======**

**<< Welcome to ElaStic_1.0 >>**

**This software package allows you to obtain full second-order elastic tensors (elastic constants)**

**for all crystal lattice types and third-order elastic constants for cubic, hexagonal, and**

**rhombohedral crystals.**

**This code is written in Python programming language and uses the SGROUP tool as symmetry and**

**space-group calculator and utilizes Exciting, Wien2k and Quantum Espresso density-functional codes**

**for energy and stress calculations.**

**DESCRIPTION**

**=============**

**In order to use "ElaStic" software package, please follow the steps below:**

**STEP 0.1:**

**The "ElaSticROOT" shell variable must be set by the user. For instance, add the following**

**line with the correct "ElaStic" path, in the ".bashrc" file:**

**export ElaSticROOT=/home/dir1/dir2/ElaStic**

**STEP 0.2:**

**Download and install "SGROUP" program:**

**This program is a utility which allows "ElaStic" to determine the space-group and symmetry**

**operations of a crystal structure. More information can be found in:**

**Programmers : B.Z. Yanchitsky, A.N. Timoshevskii**

**Download Link : http://cpc.cs.qub.ac.uk/summaries/adon**

**Journal Reference : Comput. Phys. Commun. 139(2001)235**

**You can also find "SGROUP" program in the file "adon_v1_0.tar.gz" in "ElaStic"**

**directory: Go to the "ElaStic" directory or where you saved this zipped file and execute the**

**following commands ($ means command line in a terminal):**

**$ tar xfvp adon_v1_0.tar.gz**

**$ cd SpaceGroups**

**$ make**

**$ cp sgroup $ElaSticROOT**

**You can find more information about "SGROUP" program in "SpaceGroups/README" file.**

**STEP 1.1:**

**In order to generate input files for a series of distorted structure, run the following script**

**from the command line:**

**$ ElaStic_Setup**

**This program requires a structural input file which can be the same as the input file of the**

**following DFT codes:**

**exciting (http://exciting-code.org/)**

**WIEN2k (http://www.wien2k.at/)**

**Quantum ESPRESSO (http://www.quantum-espresso.org/)**

**Once the input file is ready, "ElaStic" requires these values:**

**-The order of the elastic constants which you are interested in calculating.**

**-The absolute value of the maximum strain.**

**-Number of deformed structures equally spaced between the maximum negative strain and the**

**maximum positive one.**

**Entries must be typed on the screen when they are requested.**

**STEP 1.2:**

**Calculate the energy or stress tensor of deformed structure using one of the mentioned DFT**

**codes.**

**NOTICE to "WIEN2k" users:**

**A shell script program is provided under the name "ElaStic_WIEN2k_init" which allows you**

**to initialize the deformed structures automatically.**

**Before executing this program, you must specify input variables of "WIEN2k" calculations.**

**It is recommended to copy this file to the directory where "Dst??" directories, e.g. Dst01,**

**exist. Then, modify line 23 of this program according to the accuracy of your calculations.**

**The "WIEN2k_init_lapw_silent" script is the modified script file of the "init_lapw" program.**

**You find FLAGS of "WIEN2k_init_lapw_silent" program if you write following command in terminal:**

**$ WIEN2k_init_lapw_silent -H**

**Once the WIEN2k calculations are finished, you can run the following scripts to save and clean**

**your calculations.**

**$ ElaStic_Save_Clean_WIEN2k**

**NOTICE to "Quantum ESPRESSO" users:**

**The output file must be saved under same name of the input file but with ".out" extension.**

**For instance, if a given input file is named as "Dst02_25.in", the output file must be saved**

**as "Dst02_25.out".**

**STEP 2.1:**

**In order to calculate elastic constants accurately, you have to analyze your calculations,**

**first.**

**The script "ElaStic_Analyze" allows you to analyze the dependence of the calculated**

**derivatives of the "energy-vs-strain" or "energy-vs-stress" curves on the two following**

**parameters:**

**-The range of distortions.**

**-The degree of the polynomial fit.**

**The script can be run giving the following command in terminal:**

**$ ElaStic_Analyze**

**At this point, "xmgrace" plots automatically appear on your screen. For each distortion,**

**you can find the best distortion range and the best order of polynomial fit. You can find more**

**details about these issues in "ElaStic_Paper.pdf".**

**STEP 2.2:**

**In order to obtain the numerical values of the second- and third-order elastic constants,**

**you should edit the "ElaStic_2nd.in" and "ElaStic_3rd.in", respectively.**

**In each row of these files, you should insert a value for "eta_max" and "Fit_order". According**

**to the result of the visual analysis of the figures in the previous step, these two values are**

**extracted by considering the plateau regions of the corresponding plot: "eta_max" is a value**

**of maximum distortion located in the plateau region of the curve representing the polynomial**

**fit of order "Fit_order".**

**STEP 3.0:**

**At this stage, in order to calculate elastic constants and moduli, run the following script:**

**$ ElaStic_Result**

**Numerical values of the elastic constants are output in "ElaStic_2nd.out" and**

**"ElaStic_3rd.out" files for the second- and third-order elastic constants, respectively.**

**POST-PROCESSING PROGRAMS**

**==========================**

**1- "ElaStic_xyz2XYZ" is a program to transform elastic constants from one Cartesian coordinate**

**to another Cartesian systems.**

**In order to transform elastic constant tensor from an old Cartesian coordinate system to a new**

**one, "ElaStic" requires two input files:**

**i - The output file of "ElaStic" (ElaStic_2nd.out).**

**ii- A file with "Transformation_Matrix" name. This file contains 3X3 matrix in following**

**format:**

**i'.i i'.j i'.k**

**j'.i j'.j j'.k**

**k'.i k'.j k'.k**

**where i', j' and k' are the unit vectors in the new system and i, j and k are the**

**unit vectors in old Cartesian coordinate systems. Dot (.) indicates the "dot product" of two**

**vectors.**

**2- "ElaStic_Analyze_B0" is a program to check the dependence of the bulk modulus (B0) and its**

**pressure-derivative (B0') on the range of distortion and the degree of the polynomial fit**

**parameters.**

**This program requires an input file, with an arbitrary name, which contains volume and energy**

**value in two columns.**

**REFRANCE PAPER**

**================**

**ElaStic: A tool for calculating second-order elastic constants from first principles**

**Computer Physics Communications 184, 1861-1873 (2013).**

**This article contains method, the numerical algorithm and results which are calculated with ElaStic.**

**In case of publication, if you used ElaStic for any purpose, please cite this reference.**

**CONTACT**

**=========**

**If you have any suggestion or you found any bug, please write to**

**E-mail: rostam@physik.hu-berlin.de**

**Rostam Golesorkhtabar**

**Humboldt-UniversitÃ¤t zu Berlin**

**Institut fÃ¼r Physik und IRIS Adlershof, Theoretische FestkÃ¶rperphysik**

**Zum Grossen Windkanal 6, 12489 Berlin, Germany.**

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