# 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
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