mirror of https://gitlab.com/QEF/q-e.git
56 lines
2.4 KiB
Plaintext
56 lines
2.4 KiB
Plaintext
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This example shows how to use the vdw-DF functional in pw.x, a
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method based on the one proposed by Guillermo Roman-Perez and
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Jose M. Soler in:
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G. Roman-Perez and J. M. Soler, PRL 103, 096102 (2009)
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henceforth referred to as SOLER. That method is a new implementation
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of the method found in:
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M. Dion, H. Rydberg, E. Schroeder, D. C. Langreth, and
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B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004).
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henceforth referred to as DION. Further information about the
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functional and its corresponding potential can be found in:
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T. Thonhauser, V.R. Cooper, S. Li, A. Puzder, P. Hyldgaard,
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and D.C. Langreth, Phys. Rev. B 76, 125112 (2007).
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A review article that shows many of the applications vdW-DF has been
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applied to so far can be found at:
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D. C. Langreth et al., J. Phys.: Condens. Matter 21, 084203 (2009).
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---------------------------------------------------------------------
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The example will first check if all the necessary files are present,
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and then run the simulations.
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As for this particular kind of implementation, the
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vdw-DF need a so called "vdW_kernel_table", a universal file that has to be
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generated once and used for all other calculations.
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This table, stored in ASCII format, usually ships with the QE distribution,
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in case the file is not present the example will launch the routine needed
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to generate it. It can be a long process, up to 30 mins in basic single CPU
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machine, but once generated can be used in any other machine and for any
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other calculation.
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After the check, and the possible generation, the example will proceed
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with two simulations, in particular
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1) A variable cell relaxation of a simple 1x1 graphite. The parameters
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used (such as k-point mesh and energy cutoffs) are not converged, use them
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only for test runs, increase them accordingly for production runs.
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Here the stress will be used to converge the cell at 0 pressure.
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2) A self-consistent energy calculation of a water dimer in the
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equilibrium configuration. Check the energies and forces against
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those in the reference file.
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bonus) If you have the Ar.pz-rrkj.UPF in the PP_dir, you can activate the
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last example by removing the comments from the execution lines (277-280).
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In this example it is shown how to run a BFGS relaxation of the forces
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for the Argon dimer. Check that the energies and forces agree with those
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in the reference file, and that the final positions are correct.
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