#! /bin/sh


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

# Remark: this calculation simulates unrestricted fragments using the FRAGOCCUPATIONS
# key. Real unrestricted fragments can also be 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 adf.rkf for the overall PCCP calculation are done here 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.


AMS_JOBNAME=CP $AMSBIN/ams <<eor
System
  atoms
     C         .0000    .0000    .6681
     P         .0000    .0000   2.2555
  end
end

Task SinglePoint

Engine ADF
  title cp_fpccp_asr
  eprint
    sfo eig ovl
  end
  basis
    core Large
    type TZ2P
  end
  numericalquality Good
  xc
    gga BECKE PERDEW
  end
EndEngine
eor

AMS_JOBNAME=CP_Unrestricted $AMSBIN/ams <<eor
System
  atoms
     C         .0000    .0000    .6681  adf.f=CP
     P         .0000    .0000   2.2555  adf.f=CP
  end
end

Task SinglePoint

Engine ADF
  title cp_fpccp_asu
  eprint
    sfo eig ovl
  end
  fragments
     CP   CP.results/adf.rkf
  end
  fragoccupations
     CP
     SIGMA 3//2
     PI    2//2
     SUBEND
  end
  numericalquality Good
  spinpolarization 1
  unrestricted
  xc
    gga BECKE PERDEW
  end
EndEngine
eor


AMS_JOBNAME=PCCP_pb $AMSBIN/ams <<eor
System
  atoms
     P         .0000    .0000   2.2555  adf.f=CP_A
     C         .0000    .0000    .6681  adf.f=CP_A
     C         .0000    .0000   -.6681  adf.f=CP_B
     P         .0000    .0000  -2.2555  adf.f=CP_B
  end
end

Task SinglePoint

Engine ADF
  title pccp_fa1_pb
  eprint
    orbpop 20  20
    end
    sfo eig ovl
  end
  fragments
     CP_A   CP.results/adf.rkf
     CP_B   CP.results/adf.rkf
  end
  fragoccupations
     CP_A
     SIGMA 3//2
     PI    2//2
     SUBEND
     CP_B
     SIGMA 2//3
     PI    2//2
     SUBEND
  end
  numericalquality Good
  removeallfragvirtuals
  symmetry C(LIN)
  xc
    gga BECKE PERDEW
  end
  print VDDanalysis
EndEngine
eor


AMS_JOBNAME=PCCP $AMSBIN/ams <<eor
System
  atoms
     P         .0000    .0000   2.2555  adf.f=CP_A
     C         .0000    .0000    .6681  adf.f=CP_A
     C         .0000    .0000   -.6681  adf.f=CP_B
     P         .0000    .0000  -2.2555  adf.f=CP_B
  end
end

Task SinglePoint

Engine ADF
  title pccp_fa1_as
  eprint
    orbpop 20  20
    end
    sfo eig ovl
  end
  fragments
     CP_A   CP.results/adf.rkf
     CP_B   CP.results/adf.rkf
  end
  fragoccupations
     CP_A
     SIGMA 3//2
     PI    2//2
     SUBEND
     CP_B
     SIGMA 2//3
     PI    2//2
     SUBEND
  end
  numericalquality Good
  symmetry C(LIN)
  xc
    gga BECKE PERDEW
  end
  print VDDanalysis
EndEngine
eor

AMS_JOBNAME=CP_B3LYP $AMSBIN/ams <<eor
System
  atoms
     C         .0000    .0000    .6681
     P         .0000    .0000   2.2555
  end
end

Task SinglePoint

Engine ADF
  title B3LYP restricted
  basis
    core None
    type TZ2P
  end
  numericalquality Good
  xc
    hybrid B3LYP
  end
EndEngine
eor

AMS_JOBNAME=CP_B3LYP_Unrestricted $AMSBIN/ams <<eor
System
  atoms
     C         .0000    .0000    .6681  adf.f=CP
     P         .0000    .0000   2.2555  adf.f=CP
  end
end

Task SinglePoint

Engine ADF
  title B3LYP unrestricted
  fragments
     CP   CP_B3LYP.results/adf.rkf
  end
  fragoccupations
     CP
     SIGMA 7//6
     PI    4//4
     Subend
  end
  numericalquality Good
  spinpolarization 1
  unrestricted
  xc
    hybrid B3LYP
  end
EndEngine
eor

AMS_JOBNAME=PCCP_B3LYP_pb  $AMSBIN/ams <<eor
System
  atoms
     P         .0000    .0000   2.2555  adf.f=CP_A
     C         .0000    .0000    .6681  adf.f=CP_A
     C         .0000    .0000   -.6681  adf.f=CP_B
     P         .0000    .0000  -2.2555  adf.f=CP_B
  end
end

Task SinglePoint

Engine ADF
  title PCCP B3LYP PAIRBONDING
  fragments
     CP_A   CP_B3LYP.results/adf.rkf
     CP_B   CP_B3LYP.results/adf.rkf
  end
  fragoccupations
     CP_A
     SIGMA 7//6
     PI    4//4
     Subend
     CP_B
     SIGMA 6//7
     PI    4//4
     Subend
  end
  numericalquality Good
  removeallfragvirtuals
  xc
    hybrid B3LYP
  end
  print VDDanalysis
EndEngine
eor


AMS_JOBNAME=PCCP_B3LYP $AMSBIN/ams <<eor
System
  atoms
     P         .0000    .0000   2.2555  adf.f=CP_A
     C         .0000    .0000    .6681  adf.f=CP_A
     C         .0000    .0000   -.6681  adf.f=CP_B
     P         .0000    .0000  -2.2555  adf.f=CP_B
  end
end

Task SinglePoint

Engine ADF
  title PCCP B3LYP
  fragments
     CP_A   CP_B3LYP.results/adf.rkf
     CP_B   CP_B3LYP.results/adf.rkf
  end
  fragoccupations
     CP_A
     SIGMA 7//6
     PI    4//4
     Subend
     CP_B
     SIGMA 6//7
     PI    4//4
     Subend
  end
  numericalquality Good
  xc
    hybrid B3LYP
  end
  print VDDanalysis
EndEngine
eor