# How to use the ev.x tool in Quantum ESPRESSO?

The requirement I have is to calculate the bulk modulus from the energy values at certain volumes obtained via DFT calculations. Can you provide the instructions to use the ev.x tool in the Quantum ESPRESSO code?

• Just a heads up, a meta post was made recently that is relevant to some of your recent questions and answers. Some users are concerned about the pace and quality of self-answered questions. Please weigh in on this issue when you have a chance.
– Tyberius
Oct 21 '20 at 14:31

This answer is partly based on the Computational Materials Physics Course by Stefaan Cottenier.

1. Prepare a text file with two columns, the first column being the unit cell volume (a.u^3 or Å^3) of each of your calculations, the second column being the corresponding total energy (Ry).

2. Type ev.x in the terminal, which will ask you some questions:

• Lattice parameter or Volume are in (au, Ang) Type: au.
• Enter type of bravais lattice (fcc, bcc, sc, noncubic) The type of Bravais lattice: for FCC, BCC, and SC lattices you have to specify the lattice parameter in your input text file. For all other ‘noncubic’ lattices, this should be the volume. Type: noncubic.
• Enter type of equation of state: 1 = birch1, 2 = birch2, 3 = keane, 4 = murnaghan. Type: 1.
• Input file. Type the name of your input file, e.g., EOSInput.txt.
• Output file. Type the name of your output file, e.g., EOSOutput.txt.

The output file will contain the equilibrium volume, V0, and the bulk modulus, k0, obtained from fitting a Birch-Murnaghan equation of state through your data points. The output file looks like this:

# equation of state: birch 1st order.  chisq =   0.5885D-11
# V0 =  324.74 a.u.^3,  k0 = 3006 kbar,  dk0 =  4.17  d2k0 =  0.000  emin = -260.59336
# V0 =   48.12  Ang^3,  k0 = 300.6 GPa

##########################################################################
# Vol.        E_calc        E_fit       E_diff    Pressure      Enthalpy
# a.u.^3        Ry           Ry            Ry        GPa           Ry
##########################################################################
288.10    -260.54145    -260.54145    -0.00000      46.22     -259.63621
296.70    -260.56445    -260.56445     0.00000      32.78     -259.90321
305.47    -260.58037    -260.58037    -0.00000      20.90     -260.14641
314.41    -260.58981    -260.58980    -0.00000      10.40     -260.36755
323.52    -260.59331    -260.59331    -0.00000       1.14     -260.56823
332.81    -260.59139    -260.59139     0.00000      -7.01     -260.74998
342.27    -260.58452    -260.58452    -0.00000     -14.17     -260.91416

• +1. Excellent first answer and welcome to our new community! We hope to see much more of you in the future !!! May 13 at 0:03
• Welcome to the site! Thank you for pointing out the source of this information. In a future situation like this, it would be better to either just edit the existing answer or just add a new answer rather than both. Doing both makes it unclear why there are nearly identical answers without digging into the edit history.
– Tyberius
May 13 at 19:56
• @ShoubhikRMaiti it looks like the previous answer (which I removed) was edited by this user for formatting and to report the source of the information, but then they also posted a new answer that updated the actual content.
– Tyberius
May 13 at 19:58
• I was just unable to undo the editing. Thanks for the kind clarification. :) May 14 at 1:24