mirror of https://gitlab.com/QEF/q-e.git
52 lines
2.5 KiB
Plaintext
52 lines
2.5 KiB
Plaintext
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This example illustrates how to calculate electron-phonon interaction
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c oefficients, for a (444) Monkhorst-Pack (MP) grid of q-points, in fcc Al.
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IMPORTANT NOTICE: the calculation of electron-phonon coefficients is tricky.
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Do not attempt it unless you have a clear idea of the technical problems
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(e.g. very slow convergence with k-point grid,, divergence at q=>0 for optical
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modes). Carefully read the relevant literature first.
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The calculation proceeds as follows (for the meaning of the cited input
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variables see the appropriate INPUT_* file)
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1) make a self-consistent calculation for Al using a dense grid of k-points.
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The dense grid must contain all k and k+q grid points used in the
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subsequent electron-phonon calculation and must be dense enough to
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produce accurate el-phon coefficients (in particular the double-delta
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integral at Ef is very critical). Note that you have to use unshifted
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grids (k1=k2=k3=0) only, that include k=0!
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This example uses a (16 16 16) MP grid. Note that the k-point grids
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used here are NOT dense enough for a serious calculation!!!
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The option "la2F=.true." instructs the code to save data into a
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"a2Fsave" file, subsequently read during the el-phon calculation
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(input=al.scf.fit.in, output=al.scf.fit.out)
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2) make a self-consistent calculation for Al using a grid of k-points
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that is suitable for good self-consistency and phonon calculation.
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This example uses a (888) MP grid.
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(input=al.scf.in, output=al.scf.out)
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3) make the phonon and electron-phonon calculation for the grid of q-points.
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Specify elph=.true., and the name of a file where the derivative of the
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potential is stored "fildvscf". This example uses a (444) MP grid of
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q-points (nq1=4, nq2=4, nq3=4).
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The output contains the results for the el-ph coefficient at each q-point
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lambda(q), gamma(q), and the double-delta integral at several values of
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the gaussian broadening (set in file PH/elphon.f90). These are useful
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for convergence testing.
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(input=al.elph.in, output=al.elph.out)
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The results are also written into output files "a2Fq2r.*", one per value
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of the gaussian broadening, for further use.
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4) Bring to r-space both force constants and el-phon coefficients using "q2r.x"
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Output in files "a2Fmatdyn.*", one per value of the gaussian broadening
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5) Calculate gamma on selected lines using "matdyn.x" (dos=.false.)
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6) Calculate lambda coefficient (in file "lambda") and the a^2F(omega)
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function using "matdyn.x" (dos=.true.)
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7) Calculate lambda coefficient (in "lambda.out") and Tc using "lambda.x"
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