Polyacetylene polymer calculation

Sample directory: band/e_CnHn/

This example illustrates how a one-dimensional periodic system can be treated by specifying only one lattice vector. It further shows how variables can be defined with the DEFINE keyword. The rest more or less speaks for itself. The Kspace integration is taken very accurate, whereas real space integration (ACCURACY keyword) is not so accurate.

Here and in the following BAND examples, we will leave out some space consuming parts of the input file which have been discussed already. Please check the actual input files if you wish to repeat one of the calculations.

$ADFBIN/band << eor

Title Polymer

Comment
 Technical
   Quadratic k space integration (1D)
   Low real space integration accuracy
   Definitions of variables
 Features
   Lattice   : 1D, polymer
   Unit cell : 4 atoms
   Basis     : NO+STO w/ core
End

Kspace 5   
Accuracy 3
 
Units
 Length Angstrom
 Angle  Radian
End

Define
  dCCd=1.3386
  dCCs=1.4510
  dCH=1.0770
  aCCC=124.5/180*pi
  arC=aCCC-pi/2
  aCCH=119.2/180*pi ! double bonded CC
  arH=aCCH-pi/2
End

Lattice    
dCCd+sin(arC)*dCCs cos(arC)*dCCs 0.0
End


Atoms C
  dCCd/2 0.0 0.0
 -dCCd/2 0.0 0.0
End

Atoms H
  dCCd/2+sin(arH)*dCH -cos(arH)*dCH 0.0
 -dCCd/2-sin(arH)*dCH  cos(arH)*dCH 0.0
End

A larger unit cell can of course be specified as well. In the second part of the example a supercell of 5 units is used. Another new feature introduced in this example is the TAILS keyword, which similar to ADF implies that distance cut-offs are applied to make the calculation cheaper. At the moment no big gains are yet to be expected from this, but this situation is expected to change in future versions of the code. Another keyword which is relevant for saving computer time in calculations on large systems is the NONORTHOGONALBASIS subkey

in the BASIS key. This subkey is actually mandatory at the moment if the TAILS keyword is used.

$ADFBIN/band << eor
Title Polymer with big unit cell (5 units)

Comment
 Technical
   Low quadratic k space integration (1D)
   Low real space integration accuracy
   Definitions of variables
 Features
   Lattice   : 1D, polymer
   Unit cell : 4 atoms
   Basis     : NO+STO w/ core
End

Kspace 3
Accuracy 3
 
Units
 Length Angstrom
 Angle  Radian
End

Tails Bas=1E-2

Basis
NonOrthogonalSCFBasis
End

Define
  dCCd=1.3386
  dCCs=1.4510
  dCH=1.0770
  aCCC=124.5/180*pi
  arC=aCCC-pi/2
  aCCH=119.2/180*pi ! double bonded CC
  arH=aCCH-pi/2
  Latx(nlatt)=nlatt*(dCCd+sin(arC)*dCCs)
  Laty(nlatt)=nlatt*(cos(arC)*dCCs)
  Laty(nlatt)=nlatt*(cos(arC)*dCCs)
End

Lattice    
Latx(5) Laty(5) 0.0
End

Atoms C
  dCCd/2 0.0 0.0
 -dCCd/2 0.0 0.0
  dCCd/2+Latx(1) Laty(1) 0.0
 -dCCd/2+Latx(1) Laty(1) 0.0
  dCCd/2+Latx(2) Laty(2) 0.0
 -dCCd/2+Latx(2) Laty(2) 0.0
  dCCd/2+Latx(3) Laty(3) 0.0
 -dCCd/2+Latx(3) Laty(3) 0.0
  dCCd/2+Latx(4) Laty(4) 0.0
 -dCCd/2+Latx(4) Laty(4) 0.0
End

Atoms H
  dCCd/2+sin(arH)*dCH -cos(arH)*dCH 0.0
 -dCCd/2-sin(arH)*dCH  cos(arH)*dCH 0.0
  dCCd/2+sin(arH)*dCH+Latx(1.0) -cos(arH)*dCH+Laty(1.0) 0.0
 -dCCd/2-sin(arH)*dCH+Latx(1.0)  cos(arH)*dCH+Laty(1.0) 0.0
  dCCd/2+sin(arH)*dCH+Latx(2.0) -cos(arH)*dCH+Laty(2.0) 0.0
 -dCCd/2-sin(arH)*dCH+Latx(2.0)  cos(arH)*dCH+Laty(2.0) 0.0
  dCCd/2+sin(arH)*dCH+Latx(3.0) -cos(arH)*dCH+Laty(3.0) 0.0
 -dCCd/2-sin(arH)*dCH+Latx(3.0)  cos(arH)*dCH+Laty(3.0) 0.0
  dCCd/2+sin(arH)*dCH+Latx(4.0) -cos(arH)*dCH+Laty(4.0) 0.0
 -dCCd/2-sin(arH)*dCH+Latx(4.0)  cos(arH)*dCH+Laty(4.0) 0.0
End