Hello everyone,
Iam trying to do calculations using ev.x energy volume , but Iam not getting proper explanation in the tutorial how to make input file for it.
Can someone please guide me how to make input file for ev.x?
Attachement contaisn the silicon input file for which i want to do calculations.
Thanks,
Abhinav Nag
Dear Abhinav Nag,
I have this tutorial that might be of help to you:
8.4.2 Calculation of the energy-volume curve
For a cubic crystal, the E(V ) curve is calculated by simply varying the lattice parameter alat (or celldm(1)). Since both atomic positions and k-points are determined by sym- metry and are given in a0 or 2π/a0 units respectively, there is no need to do anything else. Make a few selfconsistent calculations at different lattice parameters around the expected equilibrium one (for Si: 5.43 rA= 10.26 a.u.), for instance: alat = 9.5, 9.7, 9.9, 10.1, 10.3, 10.5 . Write the lattice parameters and the corresponding energies in a file (for instance, ”si.dat”) in this format:
alat(1) E(1)
...
alat(N) E(N)
Run the code ev.x and provide the interactive input to get a fit:
$espresso_dir/bin/ev.x
Enter type of bravais lattice (fcc, bcc, sc, hex) > fcc
Enter type of equation of state :
1=birch1, 2=birch2, 3=keane, 4=murnaghan > 4
Input file > si.dat
Output file > si.murna
In this case we have selected the fcc crystal, Murnaghan equation of state, input from file si.dat, output to si.murna. In the output file, you will find the parameters of the fit and a comparison of calculated and fitted energies. The Murnaghan E(V ) curve is given as:
B V0 B′/(B′−1) E(V)=E0+V B′ V
and the corresponding pressure P = −dE(V )/dV is: B V0 B′
P(V)= B′ V
BV0 +1 −(B′−1)
−1
(8.1)
(8.2)
where E0, V0, B, B′ are parameters of the fit: E0 is the minimum energy, V0 is the equilib- rium cell volume (V0 = a30/4 for a fcc lattice), B is the bulk modulus: B = −V dP/dV = V d2E/dV 2, B′ = dB/dP is the derivative of the bulk modulus wrt the pressure. The code prints E0 in Ry, V0 in a.u.3, B in KBar; B′ is adimensional. Once these parameters are calculated, a smooth and accurate E(V ) curve is available for every V (in a given crystal structure). More on the Birch-Murnaghan equation on state can be found for instance here: http://en.wikipedia.org/wiki/Birch-Murnaghan equation of state.
Dear Carla You explained in such a nice way. Now Iam able to do the energy vs volume calculations.
Thanks for adding the answer.
Abhinav
how to use ev.x for orthorhombic structure,where you have three input files corresponding to three lattice parameter variations. Carla Robledo
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