Energy-Volume Curves

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< Homework 1 (2013) Overview
< Homework 1 (2015) Overview

Contents

Objectives

  • Plot an energy vs. volume curve for aluminum in a FCC crystal structure.
  • Perform a K-Point convergence study
    • Use default energy cutoff provided in the pseudo-potential file.
    • Plot equilibrium energy per atoms vs. K-Point grid
    • Plot CPU time vs. K-Point grid
    • Choose the K-Point grid that corresponds to the energy convergence of 1meV with minimum time
  • Perform a convergence study on the energy cutoff value
    • Use converged K-Point grid calculated previously
    • Plot energy vs. volume curves for 70% and 130% of the maximum energy value.
  • Using converged K-Point grid and energy cutoff value plot converged energy vs. volume curves.
  • Derive an equilibrium lattice constant and a bulk modulus from the final EV curve

Instructions

VASP Guide

Executable and Potential Files

  • Navigate to
     /cavs/general/ICME_2013/Homework_1/VASP
    • This directory contains the VASP executable and POTCAR files needed for this assignment.
    • Make sure to download the correct POTCAR file specific to each group.

VASP Input Files

  • Copy the INCAR and KPOINTS inputs from here to the VASP directory.
  • This BASH script will generate a collection of POSCAR files.
    • Copy it and store it in the VASP working directory.
  • This Evfit subroutine is called by the BASH script to fit the VASP output energy to various equations of state.
    • Copy and compile Evfit to the VASP working directory.

Modify the Portable Batch System Script

  • Modify the PBS script from the VASP walk-through by removing this line:
     mpirun -np 16 NAME_OF_EXECUTABLE
    and replacing it with this one:
     ./NAME_OF_BASH_SCRIPT 
  • Where "NAME_OF_BASH_SCRIPT" needs to be replaced by the name of the BASH script.

Convergence Studies

  • The second objective requires investigation of the the change in results due to a variation of parameters in the DFT calculations.
  • Note: The FCC runscript is a series of VASP executions over a range of lattice parameters. These convergence studies enclose that process within a secondary loop over a range of new values. In other words the whole calculation is now a nested loop and consequently will take quite a bit more time to execute.

K-Point Convergence

  • Copy this additional BASH script into a direcotry with the VASP inputs, the FCC runscript, and the PBS script.
  • Edit the PBS script to call this new K-Point variance script
  • Submit the PBS script as before

Energy Cutoff Convergence

  • Use this BASH script to vary the energy cutoff value.
  • Edit the PBS script to call this ENCUT code.
  • Vary the global break condition for the electronic SC-loop (EDIFF) and plot E-V curves

Output

The FCC run script will create a few additional output files on top of the ones that VASP already makes.

  • EvsA: A Text file containing an energy vs. lattice parameter curve in column form.
  • EvsV: A text file containing an energy vs. lattice cell volume curve in column form.
  • SUMMARY: A text file containing results for equilibrium lattice constant, bulk modulus, and energy per atom.

License

By using the codes provided here you accept the the Mississippi State University's license agreement. Please read the agreement carefully before usage.

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