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.

   # 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

