Example: Bond Energy analysis open-shell fragments: PCCP

Download PCCP_Unr_BondEnergy.run

#! /bin/sh


# This example illustrates advanced usage of the bond energy decomposition
# scheme used in ADF.

# A proper decomposition of an electron-pair bond energy requires specifying
# opposite spins for the unpaired electrons of the respective radical fragments,
# which can be done with the input key FragOccupations. The specified alpha- and
# beta-spin configurations of the radical fragments are shown in the output
# section B U I L D.

# Please note that if one neglects explicitly specifying opposite spins for the
# unpaired electrons of the fragments, each of them is treated as being half an
# alpha and half a beta electron and consequently, they enter into a spurious
# Pauli repulsive interaction. This results, among others, into the Pauli
# repulsion term being too repulsive and the orbital interaction term being too
# much stabilizing.

# The example consists of an analysis of the C-C single bond between two CP
# radicals in the four-atomic molecule PCCP. The CP fragment calculations used
# to provide the TAPE21 for the overall PCCP calculation must be done, for
# technical reasons, in the restricted mode ('cp_fpccp_asr'). The proper spins
# are then specified in the calculation of the overall molecule using the
# FragOccupations key ('pccp_fa1_as'). Note that this implies a slight
# approximation because the bond energy computed in this way refers to the
# energy difference between closed-shell PCCP and two CP radicals that are
# described by orbitals from a spin-restricted SCF calculation, which have been
# given an unrestricted occupation. In other words, the set of alpha- and beta-
# spin orbitals are identical and the effect of spin polarization is missing. In
# practice, this leads to minor energy differences with respect to the correct
# bond energy, that is, the energy difference between closed-shell PCCP and two
# CP radicals treated in the unrestricted mode, i.e., for which the set of
# alpha- and beta-spin orbitals are allowed to relax toward different solutions
# in the SCF procedure. This correction term can be computed directly by
# carrying out an unrestricted computation of the CP radical ('cp_fpccp_asu') using the
# restricted CP radical ('cp_fpccp_asr') as a fragment.

# The pure orbital interaction effect of forming the electron bonding combination
# of the two radicals can be isolated from the full orbital interaction by carrying out a
# separate calculation. In this calculation (pccp_fa1_pb) the bond energy analysis is performed in
# the absence of any virtual CP fragment orbitals, using the key REMOVEFRAGORBITALS.


$ADFBIN/adf<<eor
TITLE cp_fpccp_asr
EPRINT
SFO eig ovl
END
XC
  GGA  BECKE PERDEW
END
ATOMS
  C         .0000    .0000    .6681
  P         .0000    .0000   2.2555
END
BASIS
 Type TZ2P
 Core Large
END
NumericalQuality Good
eor

rm logfile
mv TAPE21 t21cp_fpccp

$ADFBIN/adf<<eor
TITLE cp_fpccp_asu
EPRINT
SFO eig ovl
END
XC
  GGA  BECKE PERDEW
END
ATOMS
  C         .0000    .0000    .6681  f=CP
  P         .0000    .0000   2.2555  f=CP
END
FRAGMENTS
CP   t21cp_fpccp
END
FRAGOCCUPATIONS
CP
  SIGMA 3//2
  PI    2//2
SUBEND
END
UNRESTRICTED
CHARGE     0   1
NumericalQuality Good
eor

rm TAPE21 logfile

$ADFBIN/adf<<eor
TITLE pccp_fa1_pb
EPRINT
SFO eig ovl
ORBPOP  20  20
SUBEND
END
XC
  GGA  BECKE PERDEW
END
ATOMS
  P         .0000    .0000   2.2555  f=CP_A
  C         .0000    .0000    .6681  f=CP_A
  C         .0000    .0000   -.6681  f=CP_B
  P         .0000    .0000  -2.2555  f=CP_B
END
NumericalQuality Good
FRAGMENTS
CP_A   t21cp_fpccp
CP_B   t21cp_fpccp
END
SYMMETRY   C(LIN)
RemoveAllFragVirtuals
FRAGOCCUPATIONS
CP_A
  SIGMA 3//2
  PI    2//2
SUBEND
CP_B
  SIGMA 2//3
  PI    2//2
SUBEND
END
eor

rm logfile
mv TAPE21 PCCPpb.t21

$ADFBIN/adf<<eor
TITLE pccp_fa1_as
EPRINT
SFO eig ovl
ORBPOP  20  20
SUBEND
END
XC
  GGA  BECKE PERDEW
END
ATOMS
  P         .0000    .0000   2.2555  f=CP_A
  C         .0000    .0000    .6681  f=CP_A
  C         .0000    .0000   -.6681  f=CP_B
  P         .0000    .0000  -2.2555  f=CP_B
END
NumericalQuality Good
FRAGMENTS
CP_A   t21cp_fpccp
CP_B   t21cp_fpccp
END
SYMMETRY   C(LIN)
FRAGOCCUPATIONS
CP_A
  SIGMA 3//2
  PI    2//2
SUBEND
CP_B
  SIGMA 2//3
  PI    2//2
SUBEND
END
eor

rm logfile
mv TAPE21 PCCP.t21

$ADFBIN/adf<<eor
TITLE B3LYP restricted
XC
 Hybrid B3LYP
End

Atoms
  C         .0000    .0000    .6681
  P         .0000    .0000   2.2555
End
Basis
 Type TZ2P
 Core None
END
NumericalQuality Good
eor

rm logfile
mv TAPE21 CP.t21

$ADFBIN/adf<<eor
TITLE B3LYP unrestricted
XC
 Hybrid B3LYP
End

Atoms
  C         .0000    .0000    .6681  f=CP
  P         .0000    .0000   2.2555  f=CP
End
Fragments
 CP   CP.t21
End
Unrestricted
Charge 0 1
Fragoccupations
 CP
  SIGMA 7//6
  PI    4//4
 Subend
End
NumericalQuality Good
eor

rm TAPE21 logfile

$ADFBIN/adf<<eor
TITLE PCCP B3LYP PAIRBONDING
XC
 Hybrid B3LYP
End

Atoms
  P         .0000    .0000   2.2555  f=CP_A
  C         .0000    .0000    .6681  f=CP_A
  C         .0000    .0000   -.6681  f=CP_B
  P         .0000    .0000  -2.2555  f=CP_B
End
NumericalQuality Good
Fragments
 CP_A   CP.t21
 CP_B   CP.t21
End
RemoveAllFragVirtuals
Fragoccupations
 CP_A
  SIGMA 7//6
  PI    4//4
 Subend
 CP_B
  SIGMA 6//7
  PI    4//4
 Subend
End
eor

rm logfile
mv TAPE21 PCCPpb_hybrid.t21

$ADFBIN/adf<<eor
TITLE PCCP B3LYP
XC
 Hybrid B3LYP
End

Atoms
  P         .0000    .0000   2.2555  f=CP_A
  C         .0000    .0000    .6681  f=CP_A
  C         .0000    .0000   -.6681  f=CP_B
  P         .0000    .0000  -2.2555  f=CP_B
End
NumericalQuality Good
Fragments
 CP_A   CP.t21
 CP_B   CP.t21
End
Fragoccupations
 CP_A
  SIGMA 7//6
  PI    4//4
 Subend
 CP_B
  SIGMA 6//7
  PI    4//4
 Subend
End
eor

rm logfile
mv TAPE21 PCCPhybrid.t21