mirror of https://gitlab.com/QEF/q-e.git
69 lines
3.1 KiB
Plaintext
69 lines
3.1 KiB
Plaintext
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This example illustrates how to use pw.x and ph.x to calculate phonon
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frequencies at Gamma and X for Si and C in the diamond structure and
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for fcc-Ni.
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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 (input=si.scf.in,
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output=si.scf.out)
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2) make a phonon calculation for gamma point (input=si.phG.in,
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output=si.phG.out). Note that outdir and prefix have the same
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values as in the input for scf calculation.
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Note that the q-point (the Gamma point in this case) is read
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after the namelist inputph.
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Dynamical matrix will be saved for further analysis in fildyn (whose
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default name is 'matdyn', here overwritten to si.dynG)
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The Gamma point is the ONLY one for which the phonon code can be run
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directly after the scf run (provided save file was defined).
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For all other points in the BZ a non-scf preparatory run is needed,
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as it is shown here for the X point.
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3) make a phonon calculation for X point (input=si.phX.in,
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output=si.phX.out). Note that the q-point (the X point
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in this case) is read after the namelist &inputph.
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Dynamical matrices will be saved for further analysis in fildyn
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(whose default name is 'matdyn', here overwritten to si.dynX).
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The fildyn file contains the dynamical matrices for q-points that
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are equivalent by symmetry to the q-point given in input (in this
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case the three X points), therefore when calculating phonons in the
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whole BZ the code needs to be run only on inequivalent points.
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The phonon code can perform also a 'single-mode' calculation where
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only a single atom is moved in a single direction and the corresponding
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column of the dynamical matrix is calculated. This may be useful when
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studying vibrational properties of defects and/or surfaces.
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This feature is illustrated in the following part of the test.
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4) Perform again a scf calculation for Si. Why? because the phonon
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calculation performed in the previous step has overwritten the
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original wavefunctions. This step can be avoided by saving the
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content of outdir and restoring it after step 3)
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5) make a phonon calculation at X point for a single mode
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(input=si.phXsingle.in, output=si.phXsingle.out).
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Apart from the specification of the mode to be calculated
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(modenum=3), the input is identical to case 4). The only difference
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is that fildyn is not given a name, so the default one (matdyn) is
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used. This is done in order not to overwrite the previous files.
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The total dynamical matrix is not computed and matdyn is actually
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left empty.
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6) make a scf calculation of C (described with US-PP) in the diamond
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structure.
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(input=c.scf.in, output=c.scf.out).
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7) make a phonon calculation at Gamma point for C in the diamond structure.
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Note that epsil=.true. and the response to an electric field and
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the dielectric constant are also calculated.
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(input=c.phG.in, output=c.phG.out).
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8) make a scf calculation at of magnetic fcc-Ni.
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(input=ni.scf.in, output=ni.scf.out).
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9) make a phonon calculations at X point for magnetic fcc-Ni.
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(input=ni.phX.in, output=ni.phX.out).
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