Example: NOCV: CH3 – CH3

Download CH3_CH3_etsnocv.run

Example for calculation of ETS-NOCV for unrestricted fragments. ETS-NOCV: energy analysis using the Natural Orbitals for Chemical Valence. The ethane molecule is built from two methyl radicals

First the two methyl fragments are calculated. The fragments should be spin-restricted.

$ADFBIN/adf << eor
Title CH3-CH3 built from CH3 radicals,  FULL electron calc.!
atoms cartesian
    C         0.019664   -0.034069    0.009101
    H         0.039672   -0.069395    1.109620
    H         1.063205   -0.065727   -0.341092
    H        -0.474230   -0.953693   -0.341621
end
basis
H  $ADFRESOURCES/DZP/H
C  $ADFRESOURCES/DZP/C
end
symmetry NOSYM
SCF
  Iterations 2500
  Converge 1E-6
end
xc
  gga scf becke perdew
end
endinput
mv TAPE21 t21.frag1

$ADFBIN/adf << eor
Title CH3 radical
atoms cartesian
    C        -0.703210    1.217999   -0.497874
    H        -0.723753    1.252869   -1.598316
    H        -1.746567    1.250049   -0.147169
    H        -0.208833    2.137544   -0.147653
end
basis
H  $ADFRESOURCES/DZP/H
C  $ADFRESOURCES/DZP/C
end
symmetry NOSYM
SCF
  Iterations 2500
  Converge 1E-6
end
xc
  gga scf becke perdew
end
endinput
eor
mv TAPE21 t21.frag2

Next these fragments are used in the calculation of the molecule ethane, using the key FRAGOCCUPATIONS to use an unrestricted fragment occupation for the methyl radicals, such that they are prepared for bonding. In the one fragment the singly occupied orbital will be an \(\alpha\)-orbital, and in the other fragment the singly occupied orbital will be a \(\beta\)-orbital, such that the calculated Pauli repulsion between the fragments will be small.

The keys ETSNOCV and ‘PRINT etslowdin-unrestricted’ are needed in this case to to analyze the bonding in a molecule with unpaired electrons in the fragments. The symmetry must be NOSYM.

$ADFBIN/adf << eor
Title: final [CH3]-[CH3], etsnocv activated by etsnocv and etslowdin-unrestricted
atoms
    C         0.019664   -0.034069    0.009101 f=f1
    H         0.039672   -0.069395    1.109620 f=f1
    H         1.063205   -0.065727   -0.341092 f=f1
    H        -0.474230   -0.953693   -0.341621 f=f1
    C        -0.703210    1.217999   -0.497874 f=f2
    H        -0.723753    1.252869   -1.598316 f=f2
    H        -1.746567    1.250049   -0.147169 f=f2
    H        -0.208833    2.137544   -0.147653 f=f2
end
fragments
 f1 t21.frag1
 f2 t21.frag2
end
fragoccupations
 f1
  A 5 // 4
 subend
 f2
  A 4 // 5
 subend
end
symmetry NOSYM
SCF
  Iterations 800
  Converge 1E-6
end
xc
  gga scf becke perdew
end
ETSNOCV RHOKMIN=1.e-3 EKMIN=1.5 ENOCV=0.05
PRINT etslowdin-unrestricted
end input
eor

Next 2 densf calculations, to view the natural orbitals in this method, see also the the documentation for the densf analysis program and the ADF-GUI. Input is the TAPE21 of the molecular calculation.

$ADFBIN/densf << eor
GRID MEDIUM
NOCV
 Alpha
  1
  2
  59
  60
 Beta
  1
  2
  59
  60
 END
END INPUT
eor
mv TAPE41 nocv1.t41
$ADFBIN/densf << eor
GRID MEDIUM
NOCV
  THRESH 0.01
END
END INPUT
eor
mv TAPE41 nocv2.t41
eor