1
2This example shows how to use pw.x to calculate the total energy
3and the band structure of four simple systems: Si, Al, Cu, Ni .
4
5The calculation proceeds as follows (for the meaning of the cited input
6variables see the appropriate INPUT_* file)
7
81) make a self-consistent calculation for Si (input=si.scf.{david,cg}.in,
9   output=si.scf.{david,cg}.out). The number of computed bands is internally
10   computed as half the number of electrons in the unit cell
11   (4 in this case).
12
132) make a band structure calculation for Si (input=si.band.{david,cg}.in,
14   output=si.band.{david,cg}).
15   The variable nbnd is explicitly set = 8 so that the 4 valence bands
16   and the first 4 conduction bands are calculated.
17   The list of k points given in input is the list of point where the
18   bands are computed, the k-point weight is arbitrary and is not used.
19
203) make a self-consistent calculation for Al (input=al.scf.{david,cg}.in,
21   output=al.scf.{david,cg}.out).
22   Aluminum is a metal : the smearing technique is used for the
23   calculation of the Fermi energy (a value for the broadening
24   degauss is provided).
25   The number of bands is set to a value somehow larger that half
26   the number of electrons in the cell (this is a quantity to keep under
27   control and provide explicitly if the default value is too small).
28   Marzari-Vanderbilt 'cold smearing' is used.
29
304) make a band structure calculation for Al. (input=al.band.{david,cg}.in,
31   output=al.band.{david,cg}.out).
32   The variable nbnd is explicitly set = 8.
33   The list of k points given in input is the list of point where the
34   bands are computed, the k-point weight is arbitrary and is not used.
35
365) make a self-consistent calculation for Cu (input=cu.scf.{david,cg}.in,
37   output=cu.scf.{david,cg}.out).
38   Copper is also a metal. Simple Gaussian  smearing is used
39   for the calculation of the Fermi energy. K-points are automatically
40   generated.
41
426) make a band structure calculation for Cu (input=cu.band.{david,cg}.in,
43   output=cu.band.{david,cg}.out).
44   The variable nbnd is explicitly set = 8.
45   The list of k points given in input is the list of point where the
46   bands are computed, the k-point weight is arbitrary and is not used.
47
487) make a self-consistent calculation for Ni (input=ni.scf.{david,cg}.in,
49   output=ni.scf.{david,cg}.out).
50   Nickel is a magnetic metal. A local-spin-density calculation is
51   performed by specifying nspin=2 and an initial guess for the
52   magnetization of each atomic species. This initial guess is used to
53   build spin-up and spin-down starting charges from superposition of
54   atomic charges. Methfessel-Paxton smearing of order one is used.
55
568) make a band structure calculation for Ni (input=ni.band.{david,cg}.in,
57   output=ni.band.{david,cg}.out).
58
59The above is done both for Davidson diagonalization (suffix
60'david') and for Conjugate-gradient style diagonalization ('cg').
61The code is tolerant about the presence of unnecessary information
62in the namelists so that it is not necessary to remove them from the
63input when editing the scf input to get the one for a nscf run.
64
65