mirror of https://gitlab.com/QEF/q-e.git
65 lines
3.0 KiB
Plaintext
65 lines
3.0 KiB
Plaintext
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This example shows how to use pw.x to calculate the total energy
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and the band structure of four simple systems: Si, Al, Cu, 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 for Si (input=si.scf.{david,cg}.in,
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output=si.scf.{david,cg}.out). The number of computed bands is internally
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computed as half the number of electrons in the unit cell
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(4 in this case).
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2) make a band structure calculation for Si (input=si.band.{david,cg}.in,
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output=si.band.{david,cg}).
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The variable nbnd is explicitly set = 8 so that the 4 valence bands
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and the first 4 conduction bands are calculated.
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The list of k points given in input is the list of point where the
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bands are computed, the k-point weight is arbitrary and is not used.
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3) make a self-consistent calculation for Al (input=al.scf.{david,cg}.in,
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output=al.scf.{david,cg}.out).
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Aluminum is a metal : the smearing technique is used for the
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calculation of the Fermi energy (a value for the broadening
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degauss is provided).
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The number of bands is set to a value somehow larger that half
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the number of electrons in the cell (this is a quantity to keep under
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control and provide explicitly if the default value is too small).
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Marzari-Vanderbilt 'cold smearing' is used.
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4) make a band structure calculation for Al. (input=al.band.{david,cg}.in,
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output=al.band.{david,cg}.out).
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The variable nbnd is explicitly set = 8.
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The list of k points given in input is the list of point where the
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bands are computed, the k-point weight is arbitrary and is not used.
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5) make a self-consistent calculation for Cu (input=cu.scf.{david,cg}.in,
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output=cu.scf.{david,cg}.out).
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Copper is also a metal. Simple Gaussian smearing is used
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for the calculation of the Fermi energy. K-points are automatically
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generated.
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6) make a band structure calculation for Cu (input=cu.band.{david,cg}.in,
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output=cu.band.{david,cg}.out).
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The variable nbnd is explicitly set = 8.
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The list of k points given in input is the list of point where the
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bands are computed, the k-point weight is arbitrary and is not used.
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7) make a self-consistent calculation for Ni (input=ni.scf.{david,cg}.in,
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output=ni.scf.{david,cg}.out).
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Nickel is a magnetic metal. A local-spin-density calculation is
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performed by specifying nspin=2 and an initial guess for the
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magnetization of each atomic species. This initial guess is used to
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build spin-up and spin-down starting charges from superposition of
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atomic charges. Methfessel-Paxton smearing of order one is used.
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8) make a band structure calculation for Ni (input=ni.band.{david,cg}.in,
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output=ni.band.{david,cg}.out).
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The above is done both for Davidson diagonalization (suffix
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'david') and for Conjugate-gradient style diagonalization ('cg').
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The code is tolerant about the presence of unnecessary information
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in the namelists so that it is not necessary to remove them from the
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input when editing the scf input to get the one for a nscf run.
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