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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 | This example shows how to use the vdw-DF functional in pw.x, a
method based on the one proposed by Guillermo Roman-Perez and
Jose M. Soler in:
G. Roman-Perez and J. M. Soler, PRL 103, 096102 (2009)
henceforth referred to as SOLER. That method is a new implementation
of the method found in:
M. Dion, H. Rydberg, E. Schroeder, D. C. Langreth, and
B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004).
henceforth referred to as DION. Further information about the
functional and its corresponding potential can be found in:
T. Thonhauser, V.R. Cooper, S. Li, A. Puzder, P. Hyldgaard,
and D.C. Langreth, Phys. Rev. B 76, 125112 (2007).
A review article that shows many of the applications vdW-DF has been
applied to so far can be found at:
D. C. Langreth et al., J. Phys.: Condens. Matter 21, 084203 (2009).
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The example will first check if all the necessary files are present,
and then run the simulations.
As for this particular kind of implementation, the
vdw-DF need a so called "vdW_kernel_table", a universal file that has to be
generated once and used for all other calculations.
This table, stored in ASCII format, usually ships with the QE distribution,
in case the file is not present the example will launch the routine needed
to generate it. It can be a long process, up to 30 mins in basic single CPU
machine, but once generated can be used in any other machine and for any
other calculation.
After the check, and the possible generation, the example will proceed
with two simulations, in particular
1) A variable cell relaxation of a simple 1x1 graphite. The parameters
used (such as k-point mesh and energy cutoffs) are not converged, use them
only for test runs, increase them accordingly for production runs.
Here the stress will be used to converge the cell at 0 pressure.
2) A self-consistent energy calculation of a water dimer in the
equilibrium configuration. Check the energies and forces against
those in the reference file.
bonus) If you have the Ar.pz-rrkj.UPF in the PP_dir, you can activate the
last example by removing the comments from the execution lines (277-280).
In this example it is shown how to run a BFGS relaxation of the forces
for the Argon dimer. Check that the energies and forces agree with those
in the reference file, and that the final positions are correct.
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IMPORTANT NOTE: This feature works the most accurately when Revised-PBE
(RPB of short-name "revPBE" (Zhang-Yang)) is used as the gradient correction
on the exchange part of the XC functional.
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