Confinement and tails options for copper dimer

Sample directory: band/Cu2_Confine/

This example illustrates two keywords to speed up BAND calculations and reduce the required disk space to some extent, without significant loss of accuracy. The third key NONORTHOGONALSCFBASIS option is now the default. It implies a different technical solution for the SCF equations that should not alter the results, but which should typically be faster.

The TAILS keyword implies that cutoffs will be applied to the (basis) functions. Basis functions will be assumed to be zero outside the radius where the remaining relative norm of the function is smaller than 0.00001, in this example. The shape of the function is slightly modified, in a 'soft' way, beyond the radius where the relative norm of the function outside the radius is 0.01. The Coulomb option is always recommended in this line as it gives more accurate results for core functions. The tails option works only if the NONORTHOGONALSCFBASIS option is specified, which is now the default.

The CONFINEMENT option can be specified for each atom type separately. It is based on a soft cut-off related to a distance criterion. In this sense it is quite different from the tails option. The CONFINEMENT option can be useful in itself, for avoiding near linear dependency in the basis. However, its use in making BAND calculations more efficient is primarily in combination with the tails option.

These options became available in ADF2002.03 for the first time.

$ADFBIN/band << eor

Title Copper dimer - confinement and tails options

KSpace 1

Accuracy 4.5

Basis
nonorthogonalscfbasis
end

Dependency Basis=1E-10 Fit=1E-7

Units
 Angle Radian
End

SCF
 Mixing 0.05
 Iterations 20
End

Convergence
 Degenerate default
End

DIIS
 NCycleDamp 0
 DiMix 0.15
End

Define
bbb=20
ccc=4.2
End

Lattice
  bbb bbb 0
 -bbb bbb 0
End

Atoms Cu
 0 0 0
 0 0 ccc
End

....
END INPUT
eor

The output file prints some information on how much was gained because of the tails and confinement options in various routines, for example:

Compression due to negligible tails in baspnt

max. percentage stored per node 98.23%

min. percentage stored per node 95.45%