Cu_slab: 2-dim. Periodic System

Sample directory: band/e_Cu_slab/

A two-dimensional infinite (periodic boundary conditions) slab calculation is performed for Cu. The dimensionality is simply defined by the number of records in the Lattice data block. In a 2-dimensional calculation the lattice vectors are put in the xy-plane. (In a one-dimensional calculation (polymer), the lattice vector is taken along the x-axis in the program.)

In this example, the minimal numerical basis from the DIRAC subprogram is augmented by Slater-type orbital basis functions, with the keyword BasisFunctions.

Slab calculations for metals frequently suffer from SCF convergence problems, as a result of the open valence band(s). To help the program converge it is often useful or even necessary to use some special features, such as the AllBands key. This particular key requires a numerical value (0.025 in the example) and implies that a finite-temperature electronic distribution is used, rather than a sharp cut-off at the Fermi level. The numerical value is the applied energy width, in hartree units.

The so-modified electronic distribution also affects the energy. The 'true' zero-T energy is computed, approximately, by an interpolation formula. The interpolation is not very accurate and one should try to use as small as possible values for the AllBands key so as to avoid increasing uncertainty in the results. The program prints, in the energy section of the output file, the finite-T correction term that has been applied through the interpolation formula. This gives at least an indication of any remaining uncorrected deviation of the outcome from a true zero-T calculation.

$ADFBIN/band << eor
Title Cu slab

Comment
 Technical 
   Quadratic K space integration
   Good real space integration accuracy
 Features
   Lattice   : 2D
   Unit cell : 1 atom, 1x1
   Basis     : NO+STO w/ core
   Options   : AllBands (temperature effect)
End

MaxMemoryUsage=20

Kspace 5
Accuracy 4

Convergence
 AllBands  0.025
End

Lattice
  4.822 0.0
  0.0   4.822
End

Atoms Cu
  0.0   0.0   0.0
End

AtomType Cu
Dirac Cu
  7 5 
  VALENCE
  1 0 2.0
  2 0 2.0
  2 1 6.0
  3 0 2.0
  3 1 6.0
  3 2 10.0
  4 0 1.0
SubEnd

BasisFunctions
  3 2  1.65
  4 0  1.0
  4 1  2.0
SubEnd
 
FitFunctions
  1 0 44.50
  2 0 43.48
  3 0 38.92
  4 0 33.87
  4 0 23.32
  5 0 20.07
  5 0 14.33
  5 0 10.22
  6 0  8.77
  6 0  6.43
  6 0  4.72
  7 0  4.04
  7 0  3.03
  7 0  2.27
  2 1 34.50
  3 1 25.75
  4 1 19.17
  5 1 14.36
  5 1  8.97
  6 1  6.78
  6 1  4.40
  3 2 29.15
  4 2 17.85
  5 2 11.23
  5 2  5.94
  6 2  3.83
  6 2  2.13
  4 3 19.15
  4 3  8.05
  5 3  4.37
  5 3  2.00
  5 4 13.80
  5 4  7.25
  5 4  3.81
  5 4  2.00
SubEnd
End

EndInput
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