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?
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1$\begingroup$ 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. $\endgroup$– Tyberius ♦Oct 21, 2020 at 14:31
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1 Answer
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This answer is partly based on the Computational Materials Physics Course by Stefaan Cottenier.
Follow the steps provided below:
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).
Type
ev.xin 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
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$\begingroup$ +1. Excellent first answer and welcome to our new community! We hope to see much more of you in the future !!! $\endgroup$ May 13, 2021 at 0:03
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$\begingroup$ 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. $\endgroup$– Tyberius ♦May 13, 2021 at 19:56
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$\begingroup$ @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. $\endgroup$– Tyberius ♦May 13, 2021 at 19:58
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$\begingroup$ I was just unable to undo the editing. Thanks for the kind clarification. :) $\endgroup$ May 14, 2021 at 1:24