## Online Resources for Calculating the Equation of State

#### Figure: Murnaghan Fit for Bulk Aluminum based on data from Abinit Calculations

A key part of electronic structure research is a standard calculation for a crystal structure to insure that the given pseudopotential and calculation parameters (energy cutoff, k-point grid, etc) give reasonable lattice constants and physical parameters such as the bulk modulus. I have put together a list of available utility programs for calculating the Equation of State based on energy and volume. If you know of any additional codes or resources, please let me know.

Equation of State Scripts and Codes

• Mur_Fit - A small fortran code written by Andrei Postnikov to fit volume and energy data to the Murnaghan Equation of State.
• EV - Equation of State Utility included with the Quantum Espresso package under pwtools
• Murn - Murnaghan Fit Utility developed as part of the FHI98MD code. (Windows Version)
• NRL Tips and Scripts for finding the Equation of State and Equilibrium configuration for hcp structures developed as part of the tight binding Static code at NRL. In this case, both a and c need to be varied to find the minimun energy configuration. This page also discusses a gnuplot script for finding the Birch fit to the equation of state.
• EOS Version 1.4.0 is a Fortran code that can fit data to over 7 different equation of state formulas. This code is developed by J. Kay Dewhurst and can be obtained as part of the Exciting FP-LAPW code. You can find it as a subdirectory of the src directory of Exciting.
• Murnaghan Function Definition File that I developed for the Nonlinear Least Squares Fitter in Origin 7.5. Depending on the energy and volume units you choose, you will probably need to convert the bulk modulus to GPa. The graph above was done with this script.

Aluminum Abinit Calculation Details: Energy Cutoff: 60 Ha, Monkhorst-Pack K-Point Grid 16x16x16 Pseudopotential: 13al.981214.fhi Smearing Factor: 0.05 Ha.